miller tyme: Racing will always be racing and there will never be a battery that will stay the same or not change as it matures but that being said Lipos are easy to handle and maintain plus they have very good cycle life. Yes there are some packs that are better than others but just because there are new packs coming out every month/week it doesn't mean they are better.
At the moment the Booster is about the size of a speed control but from what I understand it still fits in a 12th scale. I think we will eventually see speed controls with the booster in it.
As far as running 21.5 that would slow the car downs with sub-c packs but you still would need to run sub-c and I know many racers don't want the hassle of sub-c anymore.