The main people that could offer connections at Manchester are flybe. Given they codeshare with just about any airline they can get their hands on, I wonder realistically how much more space they can 'sub out' for a codeshare now.
I mean, CX/EK/AB/EY/AY/VS/TCX/SQ and more, I do wonder how many pax are actually their own point to point pax at Manchester now!
In terms of the USA, given how large the network is now, with Detroit looking likely to follow, connections could be sought, who would have thought in 2017 MAN would have more confirmed US destinations than the likes of DUB/MAD/BRU/FCO/MXP/BCN to name a few.