Welcome!
I don't really have any helpful knowledge about your situation. I would've loved to have the Individual Interior with M Sport, but, as you said, it isn't possible on BYO, and I hated to look too deeply into it as that would have tempted me to spend the extra $$$, which I really didn't want/need to do.
I'm not familiar with BMWs history regarding making these changes for later model years, but it does make sense to me that they might not make this available for the coupe/convertible like they do on the GC. They're really pushing the GC as the ultimate BMW, so, like the engine bump, I think they'll probably keep that GC-exclusive. Hopefully someone knows something I don't (which is very possible
) and they'll let you do it in the future.
As a 650xi coupe owner, welcome to the club, and you're going to love this car. The acceleration, traction, and handling are unreal for a GT car like this. Make sure you get M Sport and Full LEDs. The car isn't quite the same without them - especially the M Sport since you get the brilliant exhaust. I wasn't an exhaust person until this car, but BMW has somehow tunes a noise that is savage-but-not-obnoxious, if that makes sense.