It would be great to vape caffeine if it satisfied the cravings for nicotine (and would likely douse any case the FDA and State legislators had for banning it), but that would make it a story too good to be true...
I would not be all that excited to see how many stimulants I could shove into my device. After a while, won't we be right back where we started from with analogs? My guess is if big tobacco gets a hold of it, that's exactly where we'll be.