As I understand the new rules as long as you had multi crew time you with be fine. The issue is with people who got an ATPL in the old days with just the 1500hrs and 100hrs night, and never had multi crew time. Its these licences which will be renewed as CPLs with the ATPL theory intact, (Although I am unsure how you keep it intact ie with a current IR etc)when multi crew time acheived you can go back to ATPL, however as most of the holders are likely to be fairly aging instructors this is unlikely to happen.
I beleive you will also retain your IMC inbuilt priviledges as an IR(R). Allow use in A2 and EASA ac.
But I am only learning the new rules as I discover them, I could be wrong.