I would put my money on EMA, BHD and BOH.
How about Gatwick, Stansted or even Luton?
The article says cities, not airports, so I don't think any other London airport is on the cards. Besides that, does not make much sense as the new routes are about connections through AMS which are no longer available for UK residents through LHR.
Don't they already operate to INV ?
That's Flybe with a single daily flight. Not sure if it is codeshared, but in its current form it is of little use in a hub and spoke operation.
How about Cambridge?
I have thought about some more exotic destinations as well, given that KLM chose Manston over all the other, more estalbished and bigger airports I mentioned above.