The recently announced Rock Band 4 will get new instruments created by Mad Catz, but these won't include any additional features over the existing last-gen peripherals. And the will be very similar in design too, says a report in current issue of British EDGE magazine.
Developer Harmonix is quoted that "the unnecessary proliferation of expensive peripherals helped kill off the music genre, after all ... and launching with a shiny new range of essential fake instruments would be in conflict with Harmonix's current beliefs". The developer is aiming to make Rock Band 4 backwards-compatible "with every existing instrument". Only the Keytar from Rock Band 3 will not be supported, since Rock Band 4 will be focussing on guitar, bass, drums and vocals.