In terms of airlines using USPBC at MAN
AA have already said they welcome it, one would assume VS/DL would use it having up to 5 daily flights to the US. This also has TCX written all over it given their large US expansion. UA would also be a given.
The only US bound I dont see using it is TOM. They only have 3/4 weekly SFB flights, which is hardly a huge trial compared to a MAN USPBC area, so, doubt they would want to use it.
What also helps MAN is the fact the current last flight to the US departs before 2pm, as I understand the DUB/SNN facilities close at a certain time, so, MAN seems a good fit for this facility.