In the interests of full disclosure: I work for Arm and have responsibilities both on Rust and Morello. That said, I do think that Morello is a good candidate here (for whatever approach we pick), for the reasons you give. CheriBSD and the LLVM ports are quite stable enough for an experimental target.
No, I'm not volunteering to do the work.
It fits within my remit, so I can, in principle, contribute some time. I'm more familiar with Morello than with Rust's internals, though, and don't have a good feel for the amount of work required (other than that it's quite substantial). Rust-on-CHERI is a popular topic, though.