Say someone wants to get involved, but they want it to work properly for mass consumption first instead of a 'works for me' attitude. Starting one before 12.04 goes stable could be difficult with all the packages changing quite rapidly(zeitgeist is a great example, but it's all for the better).
The question, is it safe to wait or does PPA creation freeze?
There's no policy on when PPAs ever freeze or when you can create one, so it's really up to you.