I would suggest creating a small map which is simply some kind of flat rocky plain, possibly with a few objects around. This way it only needs to load one very small map in addition to the current map. I kind of imagine the warp to be like (although perhaps without the fancy graphics) in assassin's creed when someone of significance is killed. a smokey or rocky flat plain, and a blank sky. Everyone in the area is dragged in, and they will remain there until A: the person who did the dimensionwarp dies, or B: the cores timer runs out, at which point, all remaining alive players are teleported back to approximately the same position. To make it a bit more interesting, I'd say that if one of the players who was dragged in dies before the warper, then they'll just respawn in the middle of the new map. Also someone else carrying a dimension core could probably be made to be capable of reversing the effect.
I see this as a good LO tool (at least in a competitive environment) the only trouble is it also would allow for griefing, as someone could pull most of their own team into one intentionally.
I'd also suggest the player who did the warp be marked by some kind of glow or something, so that everyone knows who to shoot.