That would be an interesting synth for me too …
But how many FM enthusiasts are out there, who would buy one. FM-synthesis is a bit more complicated to get ones head around it compared to subtractive synthesis and this might be the reason, why so many musicians avoid a real FM synth in the first place.
But this said … since FM synthesis is very sensitive to modulation, an Elektron sequencer combined with a multi-operator FM-engine would be one of the most versatile sound machines on the market …