top of my list would be a bright new sampler:

8/16 (maybe also 24 ) bit sampling
gate (not trigger) for play/record
gate to select play or record
cv input for sample rate
cv input to scan through sample
separate audio outs for monitoring (which i don't need in my patches)
and playing (to avoid phasing and volume problems associated with
hearing the original signal and monitor signal together)

a stereo version would have the advantage of being usable to record cv
and gate signals for use as a sequencer.

second on my list would be essentially an arduino board mounted to a
frontplate:

midi/serial in and out
usb socket
as many ins/outs as the chip (atmel or something) provides.

cheers,

stu