I think it will be on wowinterface but I'm not sure yet. I still wonder about the issue with minor versions not being updated. If a user happens to use two or more Ace3 addons currently, is there not a risk of them conflicting? If the older version loads first, the newer version will not replace it. This might break the addon depending on the newer version.
But I suppose that's just the risk you take when using pre-release libraries (or pre-beta even). :P It is the plan to start updating minor versions once beta is out, correct?
SSArenaFrames and Afflicted both use it and are on WoWInterface, I've yet had anyone run into issues with Ace3 more likely to have the actual addon error because of something another unrelated bug. nevcairiel never mentioned anything specifically wrong from it, so I doubt it's much of an issue.
I'd imagine, some form of minors will actually get bumped when they go stable.