I do not understand what a CMS would prevent from doing (related to youtube playback)?
The positive site of an Open Source CMS (like Joomla) does make sense in the following manner:
others can keep track of progress and help (joomla is documented, and other then what you experienced with the Python subject, Joomla is very well supported on any level of expertise, it is a very (very!) active community). Although I understand that Python should be developed and expanded for any improvement to occur.
But a CMS like Joomla is a never ending WIP, ppl who have more and better experience then yourself are working on parts they are more knowledgeable in. That is not telling you that you don’t know what you do, but that a community knows more then any skilled person on it’s own.
Besides Joomla is very easy to extend and modify. There is a reason why (?is it over?) 2% (?) of the web is build on Joomla. 
When you, as apparently the main website developer atm, can’t maintain for a while or are for w/e reason not available, then others can easily step in on a standardized solution like Joomla.
(Hence due to the existing knowledge and ongoing development by the Joomla community).
Besides this, as mentioned before, there are many other benefits.
You can make any template you like, extensions for matter as Youtube playback exists, as do any other in high demand solutions (for both front end as back end). I am 100% confident that it offers anything you need and what you want to be very specific about the details in, is easy to convert or adopt.
Also is there (better) support for integration of solutions (phpbb smf galleries mediawiki, etc. etc.). :eyebrowlift2:
(wouldn’t recommend integrating solutions though)
You can give (limited) rights to ppl who contribute their own blog and upload images (or not).
Security is an other, literally thousands of skilled eyes do contribute to security.
I am not trying to sell Joomla, but am trying to sell the in my opinion best way to go to get the most out of this project.
It is not just a one time build, but an interactive ongoing investment, where with knowledge spread is interesting to help you out. Also like Blender / BGE, Joomla is Open Source and deserves the the support and feedback. :eyebrowlift:
For the domain name I think we as a community should support each other and look for existing solutions and check if these can support and contribute to each other, instead of all fishing separately in the same puddle with the same intentions.
I am providing this feedback because I believe in the cause, yet think it is like the game projects on BGE, there are many attempts, but few who succeed. Supporting existing community initiatives is one important aspect often overlooked IMO.
(Hence my earlier suggestion to communicate with gameblender.org - or any other perhaps existing BGE targeting platform)
Together we stand strong. 
If (and when) the right community decisions are made, it is more likely to gain more community support and interest. With better chances of survival and actually being able to actually make a big enough difference.
As you understood I started a project myself atm with very similar goals (not the same approach), and am willing to collaborate with existing good (great) initiatives. This most certainly is a good initiative.
And I am worried that by not using an existing CMS solution a lot of time and energy will go down the drain. A Joomla site is set up within hours, leaving time to create or modify a template, and start building on the content that matters. If you focus on making a template for joomla instead of the whole back end as well, you’ll be achieving much higher results within hours instead of weeks. And are laying a more future proof foundation.
Not trying to force you to do anything though, this is just one mans opinion. But with the best intentions: laying a good foundation that lasts the sands of time at least long enough to see not only the light of day, but to be able to actually achieve it’s goals and shine. 
(overly dramatic :evilgrin: :D)
