I really like the idea of puzzle items with secrets that can be unlocked. Have you seen the Bard's Tale kickstarter video where they show a dagger that can have poison damaged unlocked by solving a sort of "The Room"-like physics puzzle on the sword? I thought that was insanely awesome. Larian doesn't necesarilly have to do the same thing, but could do dialog interactions with items that have like 5 steps with 4 choices each, or more (so you can't just brute force the solution or save and reload a billion times if it fails after X number of tries). You have to find clues throughout the world to figure out the proper state of each lever. A sort of fantasy zebra puzzle puzzle where you use information from these clues to deduce the states of the levers could be effective.

Custom spells for unique items are a great way for them to really have a niche without necessarily having OP stats.

There's also lots of opportunities for crafting puzzles that can make loot feel cool. The Buffalo Sabre sword was cool, though I don't recall if it had much of a backstory or lore, or if it was some kind of reference.

Riddles are awesome too, but I can see translation being difficult.

I do think one issue with doing this KS before the EE comes out is I don't really know what general problems Larian has already fixed. Like, I assume talents are better balanced and hopefully there are more of them in the EE, but I could be wrong.