Playing after the end of the main story line could also allow you to see the results of your actions. You could see towns being rebuilt, talk to various NPCs and find out how things turned out for them, have people congratulate you or throw a feast in your honour, etc. In order to do this right, though, it could take a fair bit of work (extra dialog, etc) for little benefit (nice to have, but probably not missed if it wasn't in). Cutscenes during the credits could serve a similar purpose with less effort.
In one of the RPGs on the original Nintendo you could run around an talk to people after the end of the game. You pretty much just got a handful of random responses from most NPCs, but it was nice to do anyway. I'm not sure it makes sense on the scale it would need to be to stay consistent with the rest of ED, depending on what the end of the main story is.
What is the point in a mod kit anyway?Mods can range from simply adding areas or tweaking skills, monsters, balancing, etc to creating entirely separate games. Many of the mods created for Neverwinter Nights were considered superior to the official single player campaign, and helped it become more popular than it probably would have been otherwise. Of course ED isn't starting off with a weak story like NWN, but mods could still add value and extend the life of the game (if Larian does end up releasing mod tools, we may be able to play ED until DD3 is release

).