I think that IMCR holders should be required to maintain a rolling currency in the same was as the FAA IR along with 25 month revalidation.
It is rare that I find myself agreeing with BOSE on this forum, but he has made an excellent point.
Whilst unlike BOSE I think that the IMC rating is an excellent qualification and whilst I would dispute BOSE's claim that training for the rating is sub standard; the ability to fly on instruments, just like any other skill, degrades if it isn't practiced regularly.
The FAA IR has a rolling currency requirement. For those unfamiliar, the FAA require you to have logged six instrument approaches which include a hold, an intercept and VOR tracking within the preceeding six months in order for you to exercise instrument privilliges. A change to the IMC rating incorporating something like this, probably wouldn't be such a bad idea.