If I made the next Guitar Hero, I would kill myself...
I would love to make the next Rock Band, however, and add:
-Better, customizable, sound effects for the pickup switch (and have them on whenever you want)
-Music Creator + vocals recording.
-Use Natal to re-create your on-screen avatar to do exactly like you are doing. So if you are shredding on your back, so is your avatar.
-Heat/Pressure sensitive frets, instead of buttons, for the game to detect where your finger is pressing, and how hard. This would allow for you to bend/vibrato notes in addition to whammy.
-Volume and Tone knobs on the guitar, that you can screw around with while you're playing.
-As for the tracks, I would try to put a lot more new, lighter rock, like Hinder, and Linkin Park, because all of the metal songs suck so play vocals, and I think that's the reason everyone hates vocals. I love singing on rock band for all of the songs that aren't just yelling really loud so that nobody can understand you.
If i HAD to re-create guitar hero, however, I would make the slide bar down where the normal buttons are and just use them all the time, that way some songs would force you to slide with 1 finger in between playing normal notes (freebird), and you wouldn't have to move your hand up and down the guitar like your jerking it off.