One thing I'd like to see happen with the 1.8 new world - if possible - is to expand the world height. Not crazy 512, but a simpler 256. Brad mentioned above that this may not happen in the next gen, but I think it would be something that would sate a lot of players (including me) and make me want to build closer to the spawn point. The idea of traveling super-far out doesn't interest me as much as being able to build up and down without hitting limits fairly quick.
Also, I read somewhere that mobs will only drop their drops via player interaction. No lava, cacti, heights, etc. This would render mob traps obsolete, which isn't great news - I know that I for one was looking forward to building a more succinct mob trap.
