I pretty much agree with you here, and I think YouTube’s gesture is indeed very nice.
I don’t know if taking steps to ensure your content is approachable by all, etc. is necessarily going to strengthen multimedia. I view our senses and capacities as opportunities, each one giving you the chance to further express something. So, you know, using one media form over another is an important stylistic choice; not making use of a form of media in order to make a piece more accessible might weaken the true strength of the piece.
In my mind, a media project should have a singular goal to accomplish: presentation. I think factoring in every disability/accessibility could lead to a fragmentation of the work into its various mediums in an attempt to present the work to as many people as possible; by the time it’s presented, it’s too far removed from the original conception to be considered a genuine representation of someone’s work.
I’m not saying we shouldn’t aim for accessibility; YouTube’s pretty cool for what they’re attempting to do, and if a show on Netflix doesn’t have captions I actually will not watch it. Who can’t put up captions? Assholes. But as artists I think the purpose of a work is full self-expression first; full accessibility second.