I don't think it'd be possible to intelligently comment on the plan until 12.1 comes out. Broadly speaking, it should be safe to stay on an old release for a while, and it'd likely stay usable for a good while (eventually, protocols will be deprecated, but we'd probably see TrueNAS 16 before that would be any kind of a problem). The problem would be with specifics--iX doesn't do much in the way of maintenance releases on old versions, so if a showstopper of a security or integrity bug comes up in the 12.0 series after 12.1 (or 13.0, or whatever) comes out, you may need to upgrade to 12.1 to address it. But I don't know the likelihood of that, and I doubt anyone else does either.