I don't think anything could be worse than the ones they already use, namely the guitar. I don't know anyone whose Rock Band guitar still works. The strum bar is annoying enough from the onset, but slowly strumming stops working altogether. The frets are loud and uncomfortable, and, eventually, unresponsive. It's just terrible. There's really not much room for MadCatz to more poorly design a guitar.
People just end up buying GH3 controllers anyway.