I don't think you guys are looking at this accurately.
They're not going to take away a touchdown for excessive celebration AFTER a touchdown, because that's still a dead ball penalty. But say, a receiver breaks free downfield and on his way into the end zone he starts high stepping, flips into the end zone, taunts the other player with the football, etc. etc. etc., those are still live penalties and will take away the points, but most likely replay the down (maybe loss of down). It's the same as a holding call, and I think it would be a great rule if implemented that way. Players are constantly costing their team a 'meaningless' 15 yards on kickoffs in order to showboat, so you need to make the consequences big enough to where they stop. There's no room for it if you ask me.