Looking at the charted streams of snare notes (with ACCENTS) in this song [http://www.youtube.com/watch?v=C5wIfwsxAus], that just reminded me: they need to add accents on the drums like Guitar Hero: World Tour did. I mean, the stock kit and the Ion are both velocity sensitive, so by including accents, It would help clean up drum charting a little.
(I'm glad they charted the song to where you can TELL those are accents, but that only re-emphasizes the fact they need to be added. Make it to where you can turn then on and off (perhaps even optional when they ARE on, so you don't get a misstroke if the game can't tell you've accented the note), and so they're worth extra points (like the cymbal notes in Pro mode.)
This leads me to my next thought: Flams. The second stroke tends to be accented, and they also tend to be charted on two pads at once, which hints at a flam, but for those who don't quite understand, they'll play it like any other combination of two pads. Maybe the notes (when on a single pad) could be white (or purple- just whatever color), so people can tell them apart; the programmer could notate a flam on the snare or a tom (or even cymbal), but unless the person playing has flams are turned on, the game will chart them as you've normally seen them; when they ARE turned on, you see white notes.
(I'm not entirely sure about how they would go about displaying flams between pads, but I think the same idea as before (white notes) would be nice. What I'm not sure about is how one would go about displaying just WHICH pad is supposed to be played first...)