Overall ( not just content)
- ribbon controller and breath controller input ( this will be the only KB they need for oMB or band Live/Seq)/maybe a few sonds from VL7 ( addition to onboard sample playback synthesis) wouldn't hurt
- better harmonizer
-76 keys/no apeakers yet smaller foot print and light ( I know that roland does it well)
- 2 XLR /combo inputs with sepatare EFX processing ( one for vocals and the other for guitar) ( True OMB player, plays a Mid file, with realtime harmonies using midi or style track,while s playing guitar putting thru the KB's 2nd channel , clean guitar (during verse) EFX becomes dis/dlk EFX ( like automated efx)when you go to (chorus/solo part ) without worring about steping on pedals. True one man band heaven. ( harmonies and guitar solos without button pushing).

-Non spaceship design ( I still like Dx7 type clean look, Pa 3x did a good job.T4 still looks funny.

-black or gray color
- song book like features and chord sequencer without double button pressing

- still manage to put under 35-7 Ibs

-simple arps/filer sweep knobs on board ($ 200 E403 has it)

-Aduio tracks will be great ( at least drums)

-More Trio or 4 piece styles for Ac pop/rock/El rock/reggae/soft with more contemporary yet simple/not too busy drumming

- better quality hard smooth thin yet strong plastic ( faster going back to zero) wheels (Moog/Dx7 type) than can be sticky rubber wheels
.Joustick/vector would'nt hurt either for style morphoring/remixes

Thanks for asking. i don'r see Roland/Korg is doing it.