I personally think ES 5x5 is far too small.
I don't really have enough experience with different cubes to say what I'd want specifically in a 3x3, although a pillowed 3x3 would sure be nice, even if just as a gimmick.
I'm not into big cubes that much, I recently got an ES 4x4 (my rubik's brand turns like crap obviously) and I still don't solve it that much. I solved a friend's ES 5x5 once and haven't even touched my own (rubik's brand as well).
I'd like to see a more speedsolve type kit for a megaminx. I have a QJ megaminx (and a QJ pyra on the way), and I'm sure if I wanted to mod it, it'd be faster, but that would require disassembling it, probably replacing the springs, then a full lube, and the megaminx just has an insane amount of pieces for me to want to spend that much time doing it (when it takes me 10+ minutes due to look ahead fail anyway).
I love cubesmith tiles, but I dislike the fact it seems to make my 3x3's feel heavier. The three times I've tiled a 3x3 it always feels heavier than a stickered cube. I'm probably going to buy some CS stickers, possibly even the bright sets, and see what it does. What I hate about stickers is that they always end up peeling or just wearing away over time.
I agree with the Rubik's brand colors with CS quality, but again, I haven't tried CS stickers yet. I know I'd end up liking some of the brighter colors, would help with recog in darker lighting.
3x3 with rounded corner stalks, definitely a must. Why not go ahead and round out the edge pieces as well? I'm talking about the Type A / Type B cubies, not the Type F's that seem to have just the part of the edge (I haven't owned one so I might be wrong).