This is already the case in other European countries under JAR-FCL.
It varies from country to country. Some have the addition of an IRI rating, whilst others have the privileges embedded into the FI rating. The limitation found in UK issued licences is a hang over from the National Flying Instructors rating and occurred because the CAA's software was not amended on the implementation of JAR-FCL. They have had 11 years to fix it but haven't done so. If we look at EASA Part FCL it says in FCL 905.FI(h) that an FI may teach for the IR provided they have met a specific training requirement, no mention of requiring a separate IRI rating. FCL 905.IRI refers to the stand alone IRI rating much the same as in JAR-FCL; so it is not clear either way how it will be interpreted.