I've created a custom project system based on Microsoft CPS https://github.com/Microsoft/VSProjectSystem
I'm need to turn on ReSharper support for it. I know that ".xproj" projects (ASP.NET 5) also built on top of CPS and ReSharper supports it, and the "Shader project" type also use CPS. So maybe is not too hard to add support for any other CPS-based systems.
BTW, CPS could be enabled for any regular C# project by changing project type GUID as the solution file as described here https://github.com/Microsoft/VSProjectSystem/blob/02191b00b6da83a152c118e653573068c5166869/doc/scenario/turn_on_cps_for_csharp_vb_project.md .