Its hard to argue against mod support. Most of the games I've enjoyed that had real staying power included some kind massive mod at one point or another, which gave the game a new lease on life. I think the challenge with a game like this is trying to figure out what that mod support looks like. NWN had a toolset and the whole back catalogue of D&D material to work with.. It had a DM client and was totally geared up for user customization and the multiplayer experience. What it lacked was full party control tactical combat built for the Iso view.
The decision to go with henchmen and the driving camera in the original build, put certain limits on what you could do in terms of designing dungeon crawls, trying to work with a combat system like that.
It was kind of stuck in this weird space between a small scale MMO with groups (replicating the table top experience), and a single player solo slog like the crpgs that came immediately before it, but it had an amazing toolset! Glorious customization when it came to the aesthetic dimension of the game, but invariably hit a wall in the crawl, because you couldn't really design IE style combat situations that scaled for the full party of 6.
I've always enjoyed the single player experience hack and slash for this medium. A heavy emphasis of Role Play can be fun, but I don't want to join a theater group, I want to play an engaging sp game that sucks me in and allows me to avoid other people for a few hours haha. When playing with others, it usually devolves into metagaming anyway, rather than RP, so I prefer when its just built from the ground up with the focus on the single player primarily combat/puzzle driven. But what I like most is the God mode aspect, single player but controlling the whole group. There is something a little different there, than what you have in traditional table top D&D with actual other people in the room. The first crpgs that I can remember playing before Baldur's Gate crashed onto the scene and murdered all its predecessors, were games like Might and Magic III or Xeen, Pools of Radiance and the like on the B drive (when I was like 10), where you almost always had a full party (or at least that was the eventual goal.) Other games like Ultima Online or Everquest broke with that and made it more about soloing, but I never dug that as much. I think why I liked the infinity engine games so much is because they took that idea of turn based combat and puzzle play, with a collection of 6 or more characters that you're trying to develop, and just perfected it. Neverwinter, despite being brilliantly received and well modded, (a totally unique type of thing in its way), still played more to that solo character style of combat, than it did to the Infinity style of full party combat.
I guess what I'm driving at is they should make like a hybrid of Icewind Dale and NWN, but set in this new Pillars of Eternity universe they're creating.
Go heavy focus on character creation with lots more options to define the look of the avatar, custom portraits etc, and then a toolset for generating new modules under this kind of combat system. A map generator for the world map, an expansive tileset (for dungeons), a monstrous manual for the beasts and catalogs for the npcs, an ever growing spellbook that gets updated, an infinite bag of holding's worth of weapons, armor, artifacts and other curiosities to populate those levels. Doing all the same sort of things they've done here. With the arena/stronghold mode in there too (for good measure), so you could basically play it forever.
I'm pretty sure all I want is the eternal promise of more Pillars of Eternity, which is probably easiest to imagine as a sequal that opens up major mod support. I don't know if they would go that route, but I'd be down.
The only thing left to deliver on would probably be like mounts (from horses to drakes), and the ability to seamlessly zoom out from the isometric ground view to the wizard's eye level map view, and still be able to control movement on both, just by rolling out the mouse wheel to the map. That **** would be pretty cool, if they pulled it off.