GASA,
I think that to get all 4 approach units, plus 4 sets of wrap-around, high-definition VCR screens in, would require quite a sizeable extension to the building at the base of the new EGCC tower.
The Town Hall is a much better option, as it will have a canteen, and probably many other facilities enjoyed by its present employees. PLUS, the ATCOs based there will be able to travel to work on the tram, in keeping with both Manchester Council and MAG's 'sustainable transport' agendas.