Correct me if I'm wrong but wouldn't southeastern have to foot some if not all the cost as they manage Stratford international
I'd have thought that the financial responsibility for finishing off the international platforms would ultimately lie with the DfT/Her Majesty's Government, even if on paper it is filtered through any TOC.
Given the problems of not being part of Schengen, I could theoretically see Manchester Piccadilly being suitable for all the immigration gubbins that would go along with international services.
The two platforms (10 & 11 I believe) in the main trainshed either side of the travelators to P13/14 may have space for passport control etc,
if a suitable business-case could be made and the aforementioned travelators could be relocated (perhaps the 'Down' to P12 and the 'Up' to P8&9). Platform and station-throat capacity for the main trainshed may well become available after the 'Northern Hub' work is complete.
Additionally from an economic perspective Manchester has for more chance of being able to sustain such a service than York. I'd imagine that only Birmingham; Manchester; Glasgow
or Edinburgh; and possibly Cardiff will ever have the economic/cultural/political importance to support regular international services- and probably even then not sufficient to fill a full-length E* set.
One thing in favour of York (and Leeds) is that 373/3s have at least operated there in service, but that's really only a technicality I'd have thought. Given that a great big depot was built for the NoL sets at Longsight, it'd be an oversight of massive proportions* if the sets weren't built in-gauge to the routes they were planned to operate on!
* Then again, they
built the damn things! :roll: