@[email protected] @[email protected] manifest V2 is spread all over chromium source. There's definitely a way to maintain it but it'll quickly become a hassle especially between Chromium version bumps. In any case, if they said they'll do it that's still better than nothing.
As for uBlock... I don't think there's anything special to Chromium's version of Manifest V2 that they'll need to support. So it should "just work".
@[email protected] according to your threat model, of course.