If YouTube was subscription only, hypothetically, I would just not use it, and my life would be same as it is now.
There are a great many services that are nice to have, but very few I would bother paying for out of my wallet. Given the choice of paying for them or not using them, I would just walk away from most of them.
People are curious creatures indeed.
It's more money. Why would they refuse more money? It's so fucking frustrating too.
The truth is that Youtube is a parasite. They don't create free content, they have inserted themselves between regular people creating free videos and you and are demanding that you pay them for access to what would have existed without them.
From the viewers' side, there was no place to go and browse videos, you were limited to short embedded clips or had to download the entire file first.
Youtube was a game changer when it first appeared and Google hadn't yet acquired it.
I'd bet the ratio of time I have spent legit learning something useful vs just using it as distraction/entertainment ("educational" channels are often just entertainment for nerds like us)/background, it has to be something like 1000 to 1. I wouldn't need to replace the 999 at all. I guess I would read books a bit more, probably get a lot more done on personal projects, go out a bit more etc.
Not clear at all my life would be worse off except in that pinch where I need to know how to disassemble & fix the thing, right now.
It is though. Videos with "limited ads" (as it's technically called in YouTube Studio) applied to them still get paid out of Premium views.
But for the most part - probably nothing. For everything else, it'd just be either some other free option, or like going back to the internet of the early 2000s, which would be good and bad in its own ways.
As for content, it depends what you're looking for. For me, I'm mostly into maths and physics and there are so many channels and lecture series that were immensely helpful. For example, I recently went through this playlist on Lie Groups [0].
[0] https://youtube.com/playlist?list=PLN_4R2IuNuuRgJb00X2J53Iq9...
That being said, lately YT has way too many ads for my liking; thus I am using Reddit more and more for these things.