With all the modern EMUs coming on stream this does seem to make sense paths through new street given, give it to LNW franchise and run as 8 car from Manchester Airport to Birmingham airport via Piccadilly and International. The wm fleet could even retain some of the 350/2 fleet albeit refurbished to 2x2 for this work.
Proof house junction could be the main problem though for this though due to lack of paths.
Can't see any justification for an 8-car out of Manchester Airport to the south. The hourly 323 is scarcely busy; when there was a second hourly service it couldn't fill a 153!