It'd be totally impractical in reality, but I'd love added time to be dependent on the outcome of the time wasting that's gone before. E.g, if a team is winning 1-0 and is clearly taking the piss with time wasting to the point that the ref lets it be known to them that he's adding it all on, but then they concede an equaliser before 90 minutes, they don't then get that added time back to try and win the game again.