What this post says to me is that, because the bulk of the code is OS independent, you could make a Windows version with relatively little effort. That you say you can adapt if Apple changed course only reinforces this. No one can force you to do so, of course. But someone will and they will make the money.
BTW, Unless the user can customise the interface, the maker is dictating the design. That you choose to follow Apple's lead makes no difference, someone besides the user is dictating.
PhotoPlus is not a valid option. It is, by Serif's own admission, not truly a Photoshop rival.
I loathe the subscrition model and choose not to go the the CC and am hoping for a real replacement.
I find your company's decision regrettable and believe you are missing an opportunity. I honestly wish you success, though, regardless of this decision.