Right, the gist of this topic is for the OP and/or subsequent posts to mention and/or link to games outside of Roguelikes in general that, for whatever reason, happen to have what you reckon to be nifty ideas that have gone at least somewhat undeveloped period ever since said game came to be---to say nothing of not being considered for Roguelike systems to add more flavor if not be a central theme to an entire work. Can't let nifty notions outright, even if perhaps horribly flawed in their premier showcase, slip through the cracks now can we? I'll start with some off the top:
Aidyn Chronicles: The First Mage N64: Lunar/Solar(Nocturnal/Diurnal) Aspects for characters. Plenty of Roguelikes and RPG's incorporate any number of things from the gist of animal and human condition---but only has this instance in this game sought to make something out of it.
Chaos Seed for SNES/Saturn: http://www.hardcoregaming101.net/chaosseed/chaosseed.htm The notion of a dungeon wrought with underlying, synergistic/antagonistic mechanics beyond a general happenstance amid a few core rules. Really, the article should elucidate the gist I'm getting at to ye.
Deathtrap Dungeon PSX/PC: Trap-hell. While traps are prominent in Roguelikes, rarely do the traps integrate with what happens in the course of a floor in substantial/long lasting ways---or even just be quite interactive in the variety.
Spectral Souls: Resurraction of the Ethereal Empires PSP: Inventing skills/powers. This one in particular really jumps out to me as a logical thing to be tinkered with and taken to ridiculous levels in Roguelike form. Most other things are composed of parts random and otherwise afterall. Besides, who among us didn't mix Lego's with K-Nex and such to make things that simply should not have been?...
Shiren the Wanderer DS: The Food and Trap Dungeons...mainly food. Surely some great things could be done with these in the PC Roguelike landscape with these as focal points of gameplay moreso than just features among many as it generally happens.
King Arthur: the RolePlaying Wargame PC: Taking a mythological scenario and zeroing in on it while adding own flavor in a detailed and focused manner. There is a rich abundance of myths and legends across the world that could serve as an excellent, focused backdrop for an excellent Roguelike experience---many more having gone unused than used in games period. Also, it uses an ambitious system for arms and armor that serves to, in my opinion, openly mock how it is ususally considered for most RPG's and Roguelikes---whether they can nail the implementation or not this idea DEFINITELY needs to be ran with in some directions. Here's a video where they breifly explain the gist of it, though I forget which part:
http://www.gametrailers.com/video/extended-heroes-king-arthur/57954