Personally speaking, I’ll still default to public for my side projects. But a free private repo sounds like exactly the thing for online classes or web challenges where you’re explicitely asked not to share your code. I’ve just started on the cryptopals challenges, now I know where to put my code :D
Open source is just as much a culture. I don't mind fewer repositories without a LICENSE.
I suspect people who wanted free private hosting used gitlab or bitbucket.
Hopefully others will be like me and simply opt to not use it.
Besides, I wouldn't want to live in a world where people want to do X (private repos) but are forced to do Y (public repos) because X is not feasible. Now X is feasible and the landscape will more accurately reflect developer intentions.
I think the projects that could go either way -- that are public just because it's cheaper than private -- probably aren't that common or that important.