New long haul routes are no doubt a great thing, but I hope new entrants have time to establish themselves before further new additions risk cannibalising customers; especially where they compete for connecting customers.
In terms of a new long haul route with an airline which operated previously, all I can think is:
Malaysian Airlines:
possible, though KL is not high yield traffic, is it? With competition from ME3, plus Cathay and SA, might be tricky to justify such a long haul route with all its associated costs at a time of turbulence for the airline
Air India:
Always possible and BHX flights have not been pulled by the airline, suggesting a possible confidence that AI has in UK non-London airports. MAN doesn't have the same Indian VFR traffic as BHX, but perhaps there is sufficient business links to make a Delhi flight viable and there is no direct competition
South African:
I'd love it, but I doubt it. The lack of an sub-Saharan African airline (Kenyan, Ethiopian) at MAN is a hole, I believe, but I don't have confidence SA will be the ones to plug it.
El Al:
Not quite long haul, but I'm surprised that they leave the route to easyJet. They have operated the route before.
Gulf Air:
A very competitive market and they are not doing well, but I could see them wanting a piece of the pie.
My guess would be Air India, but given MAN's boom recently, it could be anyone!
Any other punts?