The Mill does good with a lot of things 🙂
Seriously, while we know that we will do a reference microkernel, the decision of which extant system to build on must wait until the new compiler is up enough to take the load, which won’t be for a while yet. It also depends on who we find as partners in the effort; if a grad student at University A gets fired up about porting system X to the Mill then we will arrange access to our tools and simulators and, eventually, hardware. We’ll also support ports by B of Y, C of Z and so on; may the best and fastest win. The Mill is intended to be policy-agnostic, so the more different systems that get ported the more confident we are in the hardware model provided. As research ports come out, we will be working to make one or another be commercial grade, or driving a merger of the most successful ideas of several.
But all that waits on the tool chain for now.