Update: Experimental .NET Core edition of Rebex components has been released with 2017 R3. See the answer above for details.
Some of our customers already expressed interest, so supporting .NET Core runtime is in our mid-term plans for 2016.
However, it is hard to promise a firm date, as currently we are busy with a HTTPS component for .NET CF that will add support for SHA-2.
We will post here once we have any news, or a beta of the .NET Core runtime binaries.