Jonathan has a plan for the meta model, and wants to prototype it in .NET anyway, so at least for the planned .NET backend we have a way forward.

Update: After some discussion with jonathan, I should clarify that the meta object model is going to be moved from Rakudo to NQP, and built on top of some primitives, which are rather portable between different VMs. So the hard part of the metamodel port need to be done only once.