What about a sorcerer class that was support oriented, adding temporary elemental effects to the other heroes' weapons, having a passive AoE like Aura that can encompass other adjacent heroes, or creating illusions that monsters MUST attack first? Just avoid the Rune weapon issue completely.
I love the idea of "elemental effects", but Descent really doesn't do the whole "different kinds of damage"-thing, and unfortunately, each expansion "has to" be practically self-contained in itself and Core, meaning that you can't pull on conditions such as Burning or Weakened to act as mechanical vehicles for the narrative concept (Burning for Fire, Weakened for Earth, Immobilize for Water/Frost, etc? Or whatever).
That being said, I'd love something like that. I'd probably call BS on the idea of creating illusions that the monsters must attack, though. Neither the heroes nor the overlord should ever be put into a purely reactionary stance, if it can be avoided. Having to make a certain decision in the interest of winning is psychologically different from being forced to do something. That sounds like a railroad to Nofunville.
Personally, unrelated to your overall idea, my wish has always been to get a Pyromancer class into the game, bundled with an appropriate hero. I'm thinking a focus on blasting, throwing the Burning Condition around like candy, and generally being a liability to your friends if you don't know what you're doing. Auras are sorely underused, and I think that adding Surge to Burn on all nearby hero weapons could be a pretty cool part of a skill. But that's unlikely to happen, because the Burning Condition was apparently in Lair of the Wyrm and will never appear again. Because reasons.
Edited by Luckmann