Thank you for the encouragement everyone
I've worked on this for a few hours and thrown together a working runtime.. it's a bit hacked as I had to pull out any of the HLSL stuff, and rewrite alot of runtime drawing functions, but it works.
So far rotations are working and relatively fast, alpha channels working fine, and I can play templates like simple platformer no problem.
The biggest challenge is going to be changing some parts of the runtime for other platforms, I noticed some Windows APIs which might be difficult.
If all goes well I'll put up a preview runtime for people to try and make sure it works for them in the next few days.