Lawyer by day. Rules lawyer by night.
If you change something too far from its original base, you lose what made it popular. That's a problem with a lot of remakes in other mediums. The factions are an integral part of planescape. Greyhawk has to have it racial tensions and International rivalries. Mystara needs It's Cold War. You start changing these that people aren't going to like them because you've changed What drew them to it in the first place.
If you want to reintroduce these to younger players, showcase the features that made them great. Older players aren't going to mind if you rehash as long as they get to play in their favorite settings again.