The EADT are reporting that GA have said that the 755s will enter service at the end of next month https://www.eadt.co.uk/news/24-new-greater-anglia-trains-arrive-1-6147956 with the class 745s in service by the autumn.
“Greater Anglia is has now taken delivery of 24 of its new trains from Swiss company Stadler - and the first are expected to enter passenger-carrying service from the end of next month.”
Time I made the effort to take a ride on the 37 + MK2 set before it's too late.
Will also be looking to try out the new trains as soon as possible. They look great.