I would like to see someone (?KLM) do NCL-Frankfurt as it sounds as though that is as big a hub as anywhere in Europe, including LHR.
More plausible than some of the sillier destinations suggested, but why KLM? They are not members of Star Alliance, and therefore as a hub it's pretty useless to them, and anyway all they'd be doing is diluting business from their AMS operation.
Benefit that NCL has over airports such as BHX is that it has a connection to the UK hub (LHR) by it's principal airline - BA, and this somewhat reduces the demand for hubbing in FRA. Also, FRA is one of the less appealing airports to transfer through - I used to do it a lot so I know!