I think one of the simplest things that can be changed is instead of requiring the largest parties from each community to do a power sharing deal, allow the two largest parties to do a deal with a smaller party from the other community (ie. SF-UUP or DUP-SDLP) or allow for the smaller parties to do a deal with each other (ie. UUP-SDLP-APNI). Would mean that the government is still 'cross-community', whilst allowing for different government options should the largest parties not be able to reach an agreement.
Although I'd go one step further and allow normal coalitions, they've got plenty of strands of opinion and given that no side really has a majority there's no point continuing this cross community stuff. That would focus them a bit: make a deal or you won't get the trappings of office.
Only just seen this. It's an interesting point. It would require national PR which would stop the pork barrelling - the reality would be that the Alliance party would have considerably more influence