To even make warbands into a Bonus XP minigame would devalue, kill and probably slaughter 50% of the current warbanders.
Also, the damage has already been caused so much in warband skills that to do this would be pretty pointless.
In all honesty, I love doing warbands with my FC, not only do we get to have fun, get free xp but warbands is becoming more and more dangerous through FC's.
Not only this but due to the XP in wilderness coming back, it has made warbands alot more easier to "ALT" therefore this is the one major problems with warbands, people can get 75 a day through alts with no danger atm, this entirely sucks, it also makes camps empty on people actually fighting for worlds or trying to get supplies through mains ETC.
Oh well, in all honesty, I love my free farming XP, its making my 120 goal become way more achievable, I don't think limiting XP is really an issue, only for us "oldies" who have done our skills the old complicated methods, but the game has to evolve, mature and higher its XP rates, this makes people want to max more, the more that want to continue playing the game stick around more revenue, more players ETC.