No Dredmor, or else just continuing past him after he's been killed. Pulling monsters at random from the first 15 floors, but significantly increasing their stats to make them threats, with boss monsters every so often.
Well, there would have to be some other way of increasing difficulty because monster stats are getting high enough even on RotDG floors that the balance is starting to tip. But if we could get around that, and have "survival mode" be a selectable thing (like permadeath), then I think it would be a nice feature.
A Dredmor arena mode would be a sight to see. Kick some Diggles to death and you get randomly dropped weapons and items after each wave. New waves spawn offscreen so stealth and range still matter. Maybe even start with zero or one skill and gradually earn skill points with waves instead of EXP. But I digress. That's a bit drastic for a roguelike.
Infinite floors?. How about a restart to the game?. Start in the first floor and level 1 again with stronger monsters but conserving skills, money and points. There could also be new bosses and secret skills.
Tome 4 has an arena mode. I am pretty sure I have seen a couple of other rogue-like do it too. I love the idea. Here how I would picture it. At the start there is a floor with 16 rooms. The starting one and then 15 rooms with a single diggle that gives 9999999 exp and drop 500 gold. By the end of the floor you have 7.5k gold and are level 15. Then for the rest of the mode you get an alternating brax shop and 2 rooms floor with a monster zoo.
