I don't have a clue about transferring, my exams were done under JAR.
It will be dependant of the CAA's opinion who your transferring to. Again under EASA there is a huge variation on what CAA's will allow. I would suspect that you have zero chance with French or German CAA's. The Irish though seem to have run a common sense approach for a number of years which is why I suggested them. I would email them and see what they say. The worst ting they can say is no. I would like to expect all courses complete before the exit date would remain valid but the stakeholders statement currently doesn't imply that they will be. You won't be the only one in the same situation.
The sooner you start asking the questions the sooner a solution can be found. A solution before the exit date which you have to take as 29th March next year will be a lot less complicated than one after. Also remember there will be a run on people doing this and it does take time to do the SOLI transfer of medical records and license information and you have potentially the whole of Easyjet with UK licenses going to do the same thing.