>Adobe porting their Creative Suite to Linux and maybe even releasing their own branded AdobeOS Linux distribution would seem to be a massive existential threat to Apple and Microsoft both
I am going to assume you are trying to say that would never happen, but suddenly going into the operating system market with a Linux distribution is not unprecedented (Google Chrome OS) and doing a simultaneous pivot to take over a related space is not either (Amazon AWS).
And if my aunty had bollocks she'd be my uncle.