The mentality of "wasting" a B787 on ORD-MAN is surely countered by Norwegian buying a fleet of new B787s and flying them on LGW-JFK. The BA B744 fleet is capable of being used on LHR-SIN but nowadays flies LHR-JFK, capability may remain but the mission changes with the requirements of the market.
Now MAN-ORD demands modern hard product, punctuality and daily service, something the B757/B763 combo now struggles on.
The US legacy presence is taking a hammering at MAN, Delta gone after three decades (albeit with VS stepping in), AA using fag end equipment on 2/3 of their offering and UA down to a single daily B757.
I suspect Thomas Cook really stepping up has stripped a lot of the connecting traffic the network carriers depended on, Norwegian if they decide to mirror LGW ops at MAN might kill a few routes off.
Manchester is a huge business destination, it baffles me why we need to keep making that point, it just gets outshone by the insanity of Mos Eisley...er London.