Eriisa: Of course now that I think about it, a 4 player version is not really a variant - but should be an additional option to the current game (and of course an additional option to any variants that might also happen.)

I still think if a person is able to roll 2 dice every time (no bonus roll if you roll a 6 or anything like that), plus if you are able to get out on a 1 or 6 - both those things together will be able to help speed up the game. (Since the slow pace of the game at times seems to be one of the bigger complaints)