I'm surprised by this, supporting DotNetCore would be a big win as it enables cross platform support.
Running the Portability Analyzer on this (see attached output) it doesn't look like too big a job - 9/13 dll's are 100% compatible. The worst of the rest is 89% compatible.
for the remainder:
Prism - new versions support .net standard
Microsoft.Build.Utilities - a .net core version now exists https://www.nuget.org/packages/Microsoft.Build.Tasks.Core/
Renci.ssh - you may need to switch ssh libraries but since ssh is a standard protocol it should be fine
Hope you decide to undertake it in the near future and good luck if you do