I wouldn’t mind bigger speakers in the FP-90X “successor,” and I believe that with some ingenuity they could fit these into the current cabinet (if anything, make it an inch, or so, deeper).
As for the mic input, I think they should get rid of it; because this piano isn’t for singer/songwriters, but rather for pianists looking for a cheaper alternative to “cabinet-type” pianos (CLP, LX, CA, etc..). If they remove this, it’ll allow them to reallocate the money (spent on a useless mic-in), and use that money for the slightly bigger speakers, so it all works out in the end (no need to further increase the price)…..