This is supposition but...

I imagine that disabling V2 is as simple as setting a flag during compile, at present. Obviously as the rest of the code base progresses it will become less simple to enable V2 support.

From a marketing perspective, the smart play is to say that you'll continue supporting uBlock Origin and keep saying that for at least the next month or so, in order to gather up some refugees from chrome. Thereafter tell every one that your built in blocker is better than uBlock Origin anyway, and then drop support for V2.

I guess the current situation could be better if Opera and Brave coordinated among themselves a shared codebase for a patch that would allow both of them to keep v2 working. The thing is that Brave most likely doesn't actually care, they've a built in adblocker so if v2 goes away then their marketshare will increase. Opera can't do it alone because, well it is the Opera Chinese owned company after all.

I was really hopping that Microsoft would take on this, think about it, from a strategic PoV if Edge kept v2 and advertised it they could just snatch a big chunk of users from Google.