Would be nice if they didn't head East again tbh. Somewhere in South London would make a nice change, but I'm struggling to think of a suitable site.
OOC seems obvious, but much of the site might be needed for station construction (similar to the King's Cross site when St. Pancras was being extended), plus the first phase of development.
Milan has gone for a location in its outskirts, 15km or so from the centre, so perhaps Barking along the Thames is a possibility. Transport is shit there though bar the A13 and effort needed would be huge. The Lower Lea Valley somewhere between Tot Hale - Enfield Lock might be more attractive, especially if CR2 goes up there.