My attempt at explaining quats for artists:
If you read through the whole thread I post an example blend file as well, showing how you can tweak the curves of quats.
Okay, pet peeve of mine: eulers are at least as unintuitive as quats when it comes to full 3-axis rotations, because with eulers each axis’ rotation changes what the following axis’ do. The meaning of each axis is constantly shifting during the animation, which is extremely difficult to follow, and even more difficult to tweak in the animation curves to any predictable end.
If anything, quats are actually easier to figure out in the full 3-axis case, assuming you have a decent mental-model of quaternions (my favorite being the model I outline in the above link).
What Eulers are more intuitive for are single-axis rotations, and in many cases two-axis rotations as well.
This whole “quats are rocket-science beyond the comprehension of mere mortal artists” mentality is complete BS. Every artists I’ve explained quats to in-person (even self-proclaimed “stupid” artists) have grasped them easily.
Maya does the conversion on-the-fly and behind the scenes. It’s a best-of-both worlds scenario. Gimbal lock never happens, and you get to work with intuitive euler rotations.
Except that you can’t tweak the curves (bezier handles) in euler, only the values of the keys: there’s no way to convert curve-tweaking from eulers to quats. To compensate for that limitation, we’d have to introduce weird settings like “bias” and whatnot. IMO it’s much easier and more intuitive to just tweak the quat curves directly.
But in addition to that, to even be able to convert just the keyframes, Blender would have to enforce that all the quat components get keyed on the same frames. So it’s not just a simple non-destructive “view quats as eulers” feature, it actually has ramifications: Blender would have to enforce certain limitations on quats to be able to view them as eulers.
Now that’s not to say that some of these things couldn’t be done, but it will complicate Blender’s rotation model a fair amount, and IMO it would be for little benefit. I think a better solution is to simply add support for actual eulers in bones (and actual quats in objects). If artists want to work with eulers, give them real eulers. The weird quat/euler view combo isn’t terribly useful in practice in my experience.