Too bad, the 7 pin D sub (like Genesis minus 2 pins) were commonly used in Famicom clone systems. The larger Nintendo sized pins seems propriety and would have to be custom made.
To be perfectly honest, every Nintendo system ever made had proprietary connectors, while Atari/Sega used 9-pin Dsub. You know, kinda like Apple devices all have proprietary plugs while Android devices by various manufacturers used industry standard. Sony Playstation and Xbox also had proprietary plugs before they went to USB.
I guess we can consider ourselves lucky NEC used two industry standard connectors for Turbo/PCe, or we would all be gaming on three foot cables! Pity the FX had that funky 7-pin controller but the lack of aftermarket controller extensions is all about supply and demand. Had the PC-FX been released globally, and sold tens of millions, someone somewhere would be making cables for it.