I'd say something like pedal or talk box peripherals. I'll explain.
You know how guitarists use pedals to make different sounds with their gutiars, right? Well, I think that the next GH should come with some kind of pedal, kind of like Rock Band's Strat, except make it mandatory to push the pedal. There's a little indicator on the side of the notechart telling you when to push the pedal.
Then there's the talk box. As the carefully observer has noted, all Guitar Hero games lack any songs with a talk box. Using a talk box could bring in many wonders, such as a few Aerosmith and Guns N' Roses songs, and especially Peter Frampton. I haven't exactly figured out how a talk box for GH would work; it would obviously work like a regular talk box, and use the shape of your mouth to change the sound, but how that'll work on the screen is still a mystery to me.
Other ideas, comments, etc. appreciated.
Well, aside from stealing everyone Harmonix put into Rock Band and making it better, Red Octane could make a keyboard with 12 keys. 12 might be pushing it, though.
I heard in GH4, there will be a guitar with 10 frets. :O
My ideas for GH4 are guitar battles against Zakk Wylde (Ozzy Osbourne, Black Label Society) and Skwisgaar (Dethklok). I know Skwisgaar is a cartoon character, but it's still possible for him to appear in GH4.
my brother got an effects pettel for christmas for his base. it really cool. but ya, i was actually thinking about that last night.
Pedals would be cool but should be optional (ie, play expert or expert with pedals).
Talk boxes, darn, that'd be cool for a few songs. They should add Do You Feel Like I Do (Peter Frampton). That'd kickass.
Oh, and we need Zeppelin, Van Halen, and Hendrix. ASAP.
Yea pedal, or being able to make your amp sound diffrent would be cool ;D
Too bad my favorite song using the talk box is too long for a GH game. It's Pink Floyd's "Pigs (Three Different Ones)."
They probably wouldn't put an 11 and a half minute long song in there. :'(
I don't think a talk box would work all that well though, honestly.
And here's a thought: multiple pickups. Why not? Pickups can be pre-assigned differently for different songs, and you should have to switch between pickups for some songs. It wouldn't be hard, since a pickup switch could easily fit right here on the guitar.
That would be awesome, because that would let them put Mars Volta or Tool songs in there. :)