I've been thinking of doing that, actually. But since I don't really know anything about IE modding, I've just been poking around in NearInfinity. So far I managed to add effects like Stoneskin and Invisibility that were absent from PS:T and I made the Nameless One capable of ranged attacks by throwing daggers (using the animation of the Ice Knife spell).
I also restored some alternate quest solutions that were fully written, but never implemented in the game.
I think the best way would've been to port BG spells and abilities into PST and then enhance the mobs' AI to use them. Maybe using GemRB, because it already can read them all, despite their differences between engine versions. Though the difficulty involved is probably beyond a mere mortal's capabilities.
It think it goes quite beyond that. Combat (and all things it entails, items, builds or lack of, ) is simply very poorly integrated into the game.
In Planescape, why do you fight?
- experience: no, you get most of it from quests and conversations
- loot: no, you get most of it from shops/containers/etc., plus conversation-only upgrades
- money: no, see above
- challenge: no, there is none
- builds: ha ha ha
- player tactics: no, there is no need for tactics, and having very few companions with pidgeonholed roles really throttles options
- enemy tactics: no, AI is almost non existent, and enemies have very few tools at their disposal
- variety: no, encounter design is abysmal
So you fight because at least sometimes you have to. And whithin a fight, there comes the Big Question:
- Is there any reason why I shouldn't auto-attack?
And the answer is, unfortunately, no, for all the reasons already mentioned in this thread. We could also go on about how it dovetails with loot being mechanically insignificant and done with a patina of weirdness for the sake of it or simply for shit'n'giggles, with how the game often attempts to overcome tropes by merely excising them, and so on.
So wouldn't it be better to get rid of combat altogether? The problem is, combat HAD to be in the game, first of all because otherwise it wouldn't perceived as a proper 'IE game'. But more importantly, getting rid of combat would mean getting rid of all the (mostly pointless) loot, of most of the leveling up mechanics, and of most of the conversation 'rewards'. And thus you'd be leaving the game with some really paper-thin gameplay: a rather clunky graphic adventure with only 'talkie' puzzles.
Mind you, with a great setting and a fantastic atmosphere, and some interesting dialogues (although mixed with a lot of cringe inducing moments when it tries to be 'philosophical'). Which in my opinion is more than enough to justify playing (and replaying) it. I mean, I'm a combatfag through and through, and my favourite game is Arcanum, which beats even Planescape for the honour of 'worst combat among RPG's that are worth playing'.