Edit: To clarify:
Is it even possible, financially speaking, to keep adding storage? I mean, advertisements don’t even make a lot of money, is the indefinite growth of server storage even sustainable?
Or will they do what Twitch does with old content and just delete them?
Tom Scott did a video on this , it is quite informative .
https://www.youtube.com/watch?v=gocwRvLhDf8
They are not going to run out of addresses , and Alphabet (google & friends) who owns youtube has massive server farms , so storage is unlikely to ever be a problem.