Thats not "will stop", that's "may stop if it becomes unsupportable". Google would have to be activly adding code that fucks with V2 support in order to make it impossible to support it. It's not gone until it's gone.
Meanwhile, in Firefox land, they had no external pressure, and continuously removed features the users wanted, despite outcry from those users.
Is Firefox the better option just because its not Chromium based? That's not clear. What is clear to me is that I don't particularly trust Google OR Mozilla to do the right thing, and (despite using Chromium as a basis for their browser), Vivaldi is doing everything I'd want a dev to do. I wouldn't put it past them to stop taking updates from the main Chromium repo and just start doing their own thing (if Chromium becomes too much of a pain to deal with).
People are complaining that having a mono-browesr is a problem, and I don't disagree, but Google and Mozilla are both assholes that don't listen to their users. Maybe we should be paying more attention to that than which codebase they use.