Earlier quoted context omitted.
Supporting Linux is a surprise, but I think it's a great move on their part. Think: How many iOS apps are frontends to a server API? And how many of those APIs are running on Linux servers? Swift on Linux means ~all the code for a client-server iOS app can be written in the same language.
Apple needs to get the rest of OS X onto the server. They could build their own servers again (unlikely), or at least license OS X Server to Dell/HP/IBM/VMWare/etc..
Now with the move of things into just the app bare bones style docker VM's in which the app is a service upon a server then maybe some form of runtime that enables some applications would be useful, maybe.
But if they went into the server market, then the trust of doing partnerships with server focused vendors would diminish. Though VMWare would probably be just as happy, if not more and that would be about it. IBM, for the arrangements they have now, work for both of them too well to upset I feel.