I called GMC today and ID check story is in simple way is this!
Candidates who have booked their exam before 2nd of October 2018 (even on 1st of October 2018) has to come to UK for ID check…
Candidates who booked their exam at 2.10.2018 or after that they will undergo their ID check at their PLAB 2 exam and day and after their PLAB 2 result is announced they need to submit documents and will be registered!
Regards!