I didn't play a lot of Gears of War, but i remember them having a horde mode, where you fought endless waves of enemies.

It'd be cool if they did this for PvP/Collosium mode. It could give crowns and heat, with each subsequent depth (costing 10 ce from each member every time you step on the party pad to spawn the next wav..or even 15-20 with bribing allowed--random crowns boost, heat boost, or items distribued) having more enemies, and harder enemies. --this would have the added benefit of rendering arena loops void. making at a managed affair.

If they wanted to make it competitive, they could pit guild teams to see who could get the deepest. or who could get the deepest in a given time frame. They could also have timed arena battles PvP. Where each team takes on Vana Duke (or jelly, or whoever) and whichever team kills the quickest wins the event. This second idea would work well b/c people would use lots of revives to try and be the quicker team to win.

Just a couple of quick, decent ideas for PvP that seemingly wouldn't be hard to implement. I'm no game designer, and thus don't understand the rigors of programmins such, but it seems like since this only involves content they already have on the game, it might be easier than creating brand new stuff, and it'd be tons of fun.