Lets be hobest here, if you live in Cornwall and want to travel around the world a airline to LHR with onward connections would be ideal, to anyone living in wherever wanting to travel to Cornwall, a flight from LHR is ideal.
Now to offer the ideal you can only really look at BA/VS/EI.
However, that's an ideal world scenario.
Reality as it is, you might well find Ryanair winning the bidding process and operating to London Liverpool.
As far as Manchester goes, yes I can see more flights being added to that route, it's already being Maintained at daily during winter 14/15 which is the first time BE have done this, however to offer this up as a decent alternative you have got to be looking at the SZ days of 2 or 3 daily to really make it viable.
Also I seriously think that an opportunity exists for EI to step into DUB-NQY, with the onward connections available on EI ex dub which could well make that route viable again.
cs