As part of the beta, we only support crypto algorithms that ship as part of OpenSSH itself, as opposed to algorithms that ship in OpenSSL/LibreSSL. Hence, we only support ed25519 in Fall Creators Update.

If you grab our GitHub bits, we compile against LibreSSL there, and you should see LibreSSL showing up in future Insider builds of Windows. That brings support for all the other crypto algorithms you'd expect (RSA, DSA, etc.)