Maybe you should use OpenTK as a backend for the engine.
What do you think?

Well, in Jade 2.0 one of the main stoppers for us was the wrapper around DX, as we tried to make our own with C++/CLI. Right now, I would use SlimDX without a second thought (for the DX part): it's stable, well maintained and it works like a charm. Something like the work Gonzo did in 1.2.