Banning slowrolls is completely pointless in my opinion. And it is actually probably wrong to do it.
Yes, it is a bad etiquette, but would you penalize a guy who doesn't say HELLO when he enters the room?
Imagine there is a rule though. It probably would be something like "Whenever you are last person to act in the hand on the river, if you have the nuts, you have 5 sec. to call, otherwise your hand will be dead" (or any other form of penalty, it doesn't matter) Do you really think that there will be no slowrolls with that rule? Wrong! Players will start doing it with second nuts, third nuts, or whatever hand they will think is pretty much a winning one.
There will always be trolls or people with bad etiquette, so best is to ignore the slowrollers, or simply not invite them to your game if this option is available.