I sold my previous pride and joy, a vintage Prophet-5, to purchase an OB-X8. I thoroughly researched the sound design parameters beforehand and have no complaints. But, I have been thinking about the one feature that the Prophet offers that the X8 lacks, namely high audio-rate modulation of the filter cutoff. I know that the OB-X8's LFO can be pushed to 50 Hz and applied to the filter (and indeed PWM). However, for each voice, the Prophet's Poly-Mod controls let you apply the frequency of Oscillator 2 to the filter chip that it's being fed through, which can yield interesting results.
I accept that this can't be done in hardware unless the circuits were laid out so as to permit it, although I can think of a way that it could possibly be done in software, were the processor sufficiently powerful. But what about a Page 2 option to let you switch the LFO into a higher frequency range, in the manner of the Buchla Music Easel? Were this possible, you could at least modulate the filter chips en masse at a high frequency, e.g. 5 kHz.