Google doesn't support new products enough to become huge and don't seem to have a cohesive plan to support a range of products in the long term.
I'm probably someone who could have benefited from Stadia but I feel like they never marketed to me in a way that even got me to try it. And the fear that this was just another experiment by Google didn't have me seeking it out on my own especially for the up front costs.
For YouTube I think it would be something like it will slowly turn into CNGooGSNBC and be heavily editorialized where you need to work with an AI assisted nebulous entity for weeks before you can upload content.
Of the two I'd bet on gmail being the dead man walking. They should full circle it and announce on an April 1st
There are 2 classes of product that I don't see them shutting down.
1. Those that make lots of money, e.g. search, youtube, maps. Unless that changes of course.
2. Those that are heavily used internally at Google, e.g. gmail, docs, calendar. They are always going to want those as internal tools. I guess they could make them internal only, but how much more work is it to maintain the public version too given it already exists?