One of the most ironic things I find about writing a Roguelike game is that the ideas for additional content never seem to stop bubbling to the surface. And that, when analysed, most of these ideas come from either other RLs, CRPGs or (especially) MMORPGs.
For example, instead of coding, I've been playing (and dying mainly) a lot of Sangband recently, and I've realised that the lack of character classes is an inspired design choice. Much has been written about classes in Roguelikes, and eventually, perhaps, I will also want to take Kharne into a classless direction. Classes are, on one hand, convenient labels/stereotypes for a character and on the other, a restrictive straightjacket preventing the character from achieving his or her true worth.
Another idea which I think might prove to add another facet to gameplay in Kharne is Reputation, which in a World of Warcraft context is:
You can gain or lose favor, otherwise known as Reputation, with many of the several different factions in Azeroth by completing certain quests or killing certain creatures. Doing so will usually unlock special rewards or new quests to accomplish.
My only concern with implementing reputation is that it can turn into a mascochistic grind very easily - there are majoring game-play balancing issues to be considered (much like Pudding Farming in fact), but a synergistic reputation system that minimises repetitiveness could add much to a RL.
Another idea, currently being discussed on r.g.r.d is that of Dungeon Morphing, dynamically changing the dungeon either independent of the player or as a response to the player's actions. Where I think this could be extremely interesting is implementing timed levels that require the player to do something in a certain period of time or else face near- or certain doom. Like in Oblivion for example.
Leaving all this side, on the development front, my current task is finishing the monster implementation, which I need to do before I can progress magic further. One of the decisions I made early in the design process has come back to bit me slightly. I've made great play (here on this blog and elsewhere) of the fact that our brave little @ is just another creature. But why does a rat, for example, need to receive the same treatment as our @ in terms of having an inventory and suchlike? And do rats really need to have Charisma stats as well as Armour and Evasion?