They could maybe implement something where every time you kill a mob of the same type, the exp decreases a little bit. For every 5 minutes you don't kill one, it goes back up. Or something like that to prevent people from bypassing guild leves all together...
I dunno, now that I type that, it doesn't sound so great.
Lancer, Fisher, Culinarian FFXI:
DRK 55, WAR 30, THF 27, DRG 27 (all retired) WoW:
Hunter 70, Warrior 29, Druid 26, Warlock 22, Shaman 19 (all retired) EQII:
Shadowknight 36 (retired)