But then if Apple gets pissed off at that, they just change the XCode EULA to say "no non-Apple hardware, please". Actually, I would not at all be shocked if the XCode EULA already says that.
But, surely it is in their business interest to make life easy for developers, especially if doing so isn't undercutting their end-user-focused hardware business? A cloud server running PureDarwin+Xcode is not undercutting their end-user-focused hardware business, and while it might mean they sell slightly less hardware units for that cloud use case (not a core market for them), surely the added ease for their developer community (who develop apps which make those end-user-focused hardware units so attractive) more than makes up for that?
They've pretty well demonstrated through questionable deprecations and hoops they make people go through with each release that ease for the developer community is not what they optimize for, but I agree it would lead to better end user experience.