There seems to be work under way for (and a status page) it: https://github.com/Microsoft/visualfsharp/wiki/F%23-for-Core...

And there's also a CoreCLR branch: https://github.com/Microsoft/visualfsharp/tree/coreclr

If anyone is interested in helping out, there is also a wiki page on how you can help port it to CoreCLR: https://github.com/Microsoft/visualfsharp/wiki/How-to-help-w...