[skohan]

You'd be surprised. There are a few reasonably well developed server-side frameworks, some of which are already used in production various places.

Also a lot of the libraries which are mostly used in iOS don't have any dependancies on the iOS platform: for instance promise or event emitter implementations etc.

IBM is actually supporting a number of open-source swift projects as well: https://github.com/IBM-Swift.

Between that and painless interop with C/C++, Swift does not feel under-supported on Linux in the least.