Only if the users follow. If users decide they won't use the mobile web then patreon and the creators they represent lose. Nobody knows for sure, but there is a general belief that users will not follow (or at least enough won't follow).

Perhaps, although that requires experimenting the new fee model first.

It's too big of a decision to take without actual numbers, and having gone through it for a few months also helps on the communication side: on the surface Patreon at least gave it a try, and there's even a chance users are pissed off enough by the new model to campaign for that change and defend the move to their fans.