To be honest once they have all their 172s, LM should go to the back of the queue for new DMUs there are others much more in need of new DMUS for differing reasons such as Northern, Arriva Trains Wales First Great Western (ex Wessex Service) could do with extra units to replace Pacer, 150 and 153 fleets. Transpennine need them as they dont have enough units and should Northern Hub come to fruition... Give some to NXEA to release the 170s and more importantly the 156s for cascade elseswhere. London Midland shoud not receive any more new trains for quite awhile IMHO,
However if we werent ordering on merit and just in a fantasy world 4 car 172s would be quite welcome at XC to replace the 2 and 3 car 170 fleet (may have to get some 3 car ones for Stansted runs though) and also East Midlands might want some for Liverpool to Norwich. Possible genuine cases for 4 cars also with first class and not on a local operator