After some NPCs in whatever town get murdered, would be kind of nice to have some randomly generated new NPCs move into town and purchase the deceased's old residents.
I'd like to see more of this in RPGs, together with other features that make the gameworld really look alive (like the wars between countries originally planned in Daggerfall).
It's really a pity that most RPGs, even the greatest ones, ultimately fail in depicting a truly dynamic world, in which you feel that something could happen even without the player being involved.
A scheduling system (done well, like in Ultima VII) is a good start, but I'd also like to see things like cities being destroyed or raided (like in the third chapter of the indie RPG Avernum, where the world perpetually changes during the war), other parties/individual beings doing quests on their own (Daggerfall was meant to have this; the
only RPG in which I've seen this implemented is Wizardry VII, where you have NPC who are actually pursuing their own schedules, travelling, fighting and doing things while you're playing, simply awesome).
Wouldn't it be cool if you simply decided not to take an quest to defeat someone because you didn't want to and then finding later that he's been killed by a NPC? That could even be done without coding an awesomely reacting AI, but simply through clever scripting: Daggerfall had something of this (the rumors that appeared after you failed a quests, but unfortunately it falls short of depicting the actual consequences - for instance, sometimes you get the rumor that a queen/king has died and has been replaced, but this has no effect whatsoever on the game.
Also my dream RPG, as already said by Martut, would include the ability to take on a job/profession and carry it over, maybe being an apprentice for someone, then gradually gaining skill and finally being able to open your own shop (which, by the way, is another great feature that is unfortunately implemented very rarely in a RPG)