Kane 1 might be retiring soon, so it'd have to be sometime soon.
Kane 2 we don't know what he's doing.
Boogeyman...well, Heyman got him over in OVW.
Will Kane run the storyline everyone thought the Ultimate Warrior was doing? Just keep him under a mask and keep replacing him every few years around May 19th and have the one that was under the mask take a few weeks off and then re-debut as a big man that now has considerable ring time under his belt and hell, he can feud with the new Kane for a while.
"Dude, there's been like 5 Kane's. Glen Jacobs died in a motorcycle crash in like 99, or steroids or some shit. Oh, and you hear this new one changed his name to Kane Kane?"
Don't know, but since you mentioned it, I had to bring this over from "comments which don't warrent a thread"