They would lose branding(the "best" Mac is this build + subscription not their top of the line model), would have to support lots of additional hardware, would

They would lose branding(the "best" Mac is this build + subscription not their top of the line model), would have to support lots of additional hardware, would have to support the setup, offer tech support, training for their support etc. . In short, not likely. Instead they may considering offering cloud instances for running XCode etc. that they can rent out.