Currently the situation is unknown.
However:
1. Grandfathering of existing IMCR privileges is highly likely.
2. EASA will release their long-delayed FCL.008 NPA in the late summer.
3. If the NPA does not include a satisfactory solution for the future of IMCR privileges within UK airspace, EASA will be told to explain their failure to the European Parliament.
4. Never say never.
Very regrettably, the UK representatives on FCL.008 failed to be sufficiently assertive regarding the IMCR. This failure must not be repeated!
However, it will be possible to continue to include the UK IMCR in 'new-style' UK pilot licences for use ONLY on Annex II aircraft with Certificates of Airworthiness (e.g. Chipmunk, Tiger Moth, Bulldog).