An alternative will be produced if youtube becomes a hassle to use. 30 years ago people watched television, but the ads became too numerous. Now only boomers watch it at all.
Nebula is trying to bill itself as an alternative, but I am not convinced it will gain the traction it needs to become what we might call a YT alternative. Users have griped about the ads on YT for years now, yet they keep using it, which just affirms that YT can inject as many ads as it wants without risking its user base. By continuing to use a product we complain about, we are giving that product permission to continue doing things we don't like.
I literally don't use the web site, but I pay for it because all the best creators are part of it, and I don't like the parasocial bullcrap that happens in patreon so it's a good alternative to support those creators more directly.
No, I don't want to pretend to be your friend in a discord chat, I want to pay your bills so you can continue pushing out a video occasionally that is incredibly well done.
Right, but what alternative? The people who pay for the production of that alternative will want to make a profit, so if you don't like the way Youtube makes a profit, be careful with assuming anything about a hypothetical future alternative.
There are already alternatives, with alternative models (Vimeo - the creator pays; Nebula - the consumer pays a subscription to watch all the content), yet YouTube remains by far the most popular.