Less bloated, more secure turnfiles!
That is, instead of sending all players everything in the game every turn and relying on the client to filter out stuff that the player can't see, create an individualized savegame for each player with only that stuff IN it in the first place! This would save lots of bandwidth and eliminate even the remotest possibility of cheating!
Also, integrated PBW support and working TCP/IP play
edit: oh, along with that, how about sane combat replays which can be calculated client-side... don't save the position of EVERY bullet 20 times per second in the savegame!!!
OK, that's a SE5 thing, not SE4, but I suspect SE4 worked the same way and we just never noticed because of the granular nature of turn-based combat as opposed to real-time!