Jamie Thompson wrote:

I was having a moment of curiosity last night about the train lengths,
and vaguely recalled (and seemed to find mentions of) platform
lengthening as part of the upgrade...but no details. Don't suppose
anyone knows any?

I can't recall details myself but the lengthening was announced on a display
next to the model carriage(s) with a promise of longer Circle and H&C
trains. However if the Mets are still going to be even longer it could
continue to cause crowd problems on the shared tracks when passengers often
have no idea which particular line train will turn up next, making it harder
to disperse them along the platform.