I have asked the CAA (yet again) to look at the requirements for IMCr/IR(R) instructors, now that it's 99% certain that the IR(R) will continue to be available for the next 5 years at least.
The AOPA recommendation is basically for the same qualifications as used to exist in halcyon pre-EASA days for the 'removal of no applied instrument' course/test and would lead to an 'IRI(Restricted)' Certificate. Similarly, for examiners, an FE who holds an IRI(R) certificate would be empowered to examine for the IMCr and IR(R).