So I've been hacking away on an Xbox target in qemu (
https://github.com/espes/xqemu). The Xbox APU contains a Motorola DSP56362 core, and there's API and tooling for applications to generate and load custom "effects" consisting of DSP code, so a reasonable emulation of it seems to be required. I imagine it makes sense to implement it as a TCG frontend, but I do not know how annoying it would be to get it wired up as a component of a device and executing alongside x86...
I'll probably be lazilly looking at this over the next few months, but if the idea is fleshed out and a mentor is available I could probably submit it as a Summer of Code proposal and if accepted be forced to be a lot more productive.