The interesting time will come when bmibaby V.2 look to replace their classic fleet, if they went down the NG route they'll be in the same boat that FR were in, an Airbus solution might be better.
v2? Why would anyone bother?
FR derate their engines hence why they couldn't fill the Boeings on the way out.
I seem to remember Baby rerating their engines to increase their performance specifically for BHD operations.
I'm sure a fully rated 73 engine could handle the City just fine.