They abandoned that specific implementation, but if you read down the discussion, it was handed off to a new thread which is still active:
If its a nice to have feature, other renderers wouldn’t have it. Imho, it is an absolute must. There is no renderer living or dead that mimics real world lighting as far as I am concerned. There is so much more to it than rendering with lights. A lot of lighting experts realize this, hence the need for light linking. It also gives you the ability to make lighting flexible especially from both a realistic and artistic approach. In the real world, there is so much light bounces that contribute to the realism that just setting up lights and hitting render isn’t good enough. You have to mimic and add those light bounces. Thats why there is lighting artist as a profession. 
I disagree, It doesn’t break the rules, because there are no rules as far as rendering is concerned to begin with. It enhances or even makes the rules better imho.
He doesn’t need examples to add it. Why is he asking for examples to add it though? The fact that every renderer has this should be enough reason to consider it. In VFX, product, archviz. Light linking makes lighting more photorealistic for those of us who have an advanced understanding of how lighting works. Renderers even now still have lighting errors as far as I am concerned, light linking fixes that.
Thanks for posting. Since 2019…sigh 
Light linking would be nice yeah and I’m also a bit surprised it still don’t exist, but personally I’d say that proper render layers would be way more useful. I started working with 3D again for a couple of months ago and I’m using Maya for rendering and I generally very much dislike it after three years in Blender, but one of the things that I really like and use all the time in Maya is it’s simple but powerful render layers where you have good overview and with overrides for everything. I do have access to light linking in Maya as well but I haven’t really had that much use for it.
I know it’s kind of the same in Blender, there are way more times that I’ve wanted proper render layers than light linking.
But sure, if they gave me light linking I would very much appreciate it 
@melvi Those two statements are not my personal point of view, but rather views held by Brecht, it seems.
I could not agree more with you. That is why I am now using K-Cycles for my latest project to control lighting better. I have always used and still use light linking in other render engines.
The light linking in kcycles isn’t really light linking is it? It seems more like layer work in the compositor.
I tried light linking in Octane which seems to behave entirely different. I could be wrong.
Correct, it is a post effect which works with masks, as far as I can tell. It updates only after rendering the preview.
Not sure about e-Cycles, though.
A good render layer system would be very welcome too.
That said, Rome wasn’t built in a day. All DCCs have their pros and cons.
Its my humble prayer he reconsiders 
. Its one of the reasons why a lot of professional lighting artists as well as those who are very particular about lighting will be reluctant to use Cycles.
Cycles X is very very fast and kudos to the Cycles team for achieving this but they should add light linking. Its a very important feature.
In terms of lighting control, I believe the new light groups produce pass information that would allow to change the lighting to an extent for artistic purposes.
Now of course, the compositing results would not be seen until after rendering is done, though I am hoping this is one thing that will change once Omar’s realtime compositor project is done.
On top of that, the fact we have Lukas Stockner as a Cycles engineer means there may be some hope for old patches to finally be finished (as he already has a good track record with commits). Some rewriting for the Cycles X architecture will have to be done though.
Thanks for the link @Herbert123
I didn’t misunderstand your words, just interested in that thread, so I can add my 2c there.
Just did some research about the light groups. I think they are going about this the wrong way. The idea of rendering the light groups at the same time is a brilliant move 
but it should be with a separate window or tab where you can link the lights to objects and vice versa.
The method of linking/grouping is too cumbersome
This guy explains it better. I guess light groups isn’t light linking? I like the ability to tweak the lights in compositing after one render but light groups could be improved upon by making it light linked which I think is in the works since you can assign light groups to meshes and you tweak the lights after rendering. But what if I want to assign two lights to one mesh?
The devs are on to something here but we need a better UI for the grouping and linking part.
Also another issue with light group is render time might be higher due to rendering the light groups into passes. So maybe Light linking should be seperate from light groups as that will render faster due to one render pass and since Cycles X is very fast, rerendering isn’t a problem.
I understand light groups is still in its early stages so it is subject to changes.
EDIT: Hmm but you can have selected objects and right click the light group tab and click copy to selected so maybe the devs are right afterall.
Yes, lights groups render different light passes, and allow you to tweak each light-group / passe in comp.
Light linking allow different lights per objects in the same render. It’s really different;
You can assign a mesh to a light group, because of emissive meshes that acts as lights. But if the object as no emission there won’t be any light contribution in the light pass.
So you can’t assign light to objects, that’s what light linking does, and you can’t have the same object or light in different light passes.
Because when you re-combine all the light passes, you’ll get a different result than the beauty. It’s not how it’s supposed to work.
There won’t be higher render time, but the render samples are split between light group passes.
You have 90 samples, 3 lights groups then each light passes get 30 samples. But when you combine them you get your 90 samples again, like in the beauty passe. If you do many tweaking with the light passes, then you’ll probably loose a bit of quality.
One way of using light groups is to separate some lights, do some adjustment in comp by using exposure value, and modifications that you can apply to your lighting (color adjustement, exposure…). So when you get a good lighting in comp, you use the same value in your 3D light, and discard the comp.
Another is, if you got a flickering light, you can separate that light in a lightgroup and animate the flickering in a compositing software, so you don’t re-render everything if you have to change the light.
But there is other cool things you can do with it !
Yeah, I know. Just got a little bit bothered with the approach the Blender devs are using which I am not really a fan of.
Ah…so thats what assigning light group to meshes was for. For only emissive objects that act as light. So that means no light linking anytime soon 
…sigh
Indeed the interface is a bit minimalistic, but I’m sure it’s possible to automate and simplify things with some addons. The base system is here at least.
I don’t know where it’s at …
Tangent animation had made a patch for that a long time ago but it was only possible with direct lighting. Due to how cycles was made, it was impossible to separate some lights and having light bounce only on particular objects.
Given that light linking is a hot topic and that cycles was recently rewritten, maybe that limitation isn’t the case anymore. One has to dig in the developers portal and blogs to know more about it I think !
But fork versions of Blender Cycles now have light linking. So what are the Blender devs doing differently though?
Sigh…I think I will have to give up hope on this ever getting added. Brecht was asking for examples of how useful it is. That means we might not see it in the next 50 years…I guess.
Ok maybe I got wrong ! And indeed I think for some time Brecht didn’t think it could be useful.
Could takes some time, but it was the same for scrambling distance, now it’s great that’s integrated even if used badly it can give really bad results !
I don’t think you got anything wrong. I think all the things you have mentioned are on point.
I will just try and be patient. I think Brecht means well. Its just that it is taking so long. Since the fork versions of Blender Cycles has this now. Its my prayer Blender won’t be far behind in getting this added.
Yess indeed ! As users it’s so long to wait for things being implemented ! Sometime like 5 years fly by between the moment things are announced and implemented … :S
But as you said, devs are quite motivated to push blender in the right direction ! That’s at least relieving !
Now I tend to take what the software has to offer and try to forget about what is missing. Without light liking it’s still possible to get nice results in some case by cheating things with options for quicker decay, light blocker… Well indeed that sounds like a nightmare , but blender push us to get technically creative, patient, in a few words, better human being… 
I agree that’s very personal and I totally understand that people get frustrated by missing feature that are quite common to every other apps …
At least the subject is on the TODO, and it looks like many people are looking forward to it and active in the design discussion… That’s at least going in the right direction !
Guys any update on light linking? not light grouping.