I also think that if there was an air link from Blackpool to London, the airlink would be prefered to a rail link.
Depends on where you land. The old Ryanair link to Stansted still meant a fairly expensive 50-55 minutes train ride for those heading into Central London (Liverpool Street station). That's without even considering check-in, security and all the associated hassles of air travel.
A direct train from Blackpool to (Central) London would take about 2h40m, based upon the current timings of Preston - London. The majority of passengers flying Manchester - Heathrow/Gatwick are either connecting onwards or heading to final destination which is closer to Heathrow/Gatwick than Euston station in Central Lonon.