Roland Perry wrote:

There is capacity today, even before displacing the outer suburbans!

Very true - although at weekends the main trainshed also gets used for
diverted Moorgate services. I was thinking more along the lines that once
the outer suburbans have started running through there will be the
opportunity to banish all "short" formations, such as the Moorgates and Hull
Trains, to the suburban trainshed (which by then will be next to the main
concourse) and reserve the main trainshed exclusively for full-length
formations.