| Shattered Galaxy has worked this way for a long time. You start on the newber planet, hit level 20 and then you can't advance until you go to the next planet. After that planet you hit the last planet. It keeps things fair in fights, and gives you a nice sense of progression for you while you're playing. It also gives you an "out" if your faction is getting curbstomped 24/7, so you go level up for a while and leave to the next one. So it helps level things out (because naturally, if you want to level you have to fight and help out your faction)
It probably only holds its sense of community due to the small userbase and lack of a need for multiple planets/servers at each tier. | 