This is true, you could bind "ulx mark" to whatever you have binded to ttt_radio, but imo this is a good suggestion to have since some people dont know about ulx mark. This is useful if people use +zoom which cant use ulx mark since it using 9 different prompts.
It sounds like a great idea, but storage for these types of files is very expensive. Video playback on websites is also taxing and expensive, as much as I want for this to be a thing somehow, I just don't think it'll be worth it. Streamable and YouTube are still great alternatives and work fine...