I lived in Exeter. First, the growth you're suggesting has to be some of the most inefficient use of land I could imagine at an airport...and look at all the fields/pieces of property you're imagining would be taken up by this ridiculous airport. Are you aware that even LHR has only 2 runways right now? The whole appeal of Devon is it's pastoral beauty, I'm not sure what paving over a huge portion of that accomplishes.
Secondly, Exeter is a tiny university town. It still has consistent train service to Bristol and London that almost anyone who wants to go to London or further afield in the UK would take (and I'll remind you, intra-UK is Flybe's core business). If you want to go somewhere else, you take the train to Bristol Airport. It's not that hard.
Thirdly, there are multiple larger cities in the Southwest that would make more sense to develop. Most obviously, Plymouth, which is both larger and features much more industry. Even still, 6 runways is goofy.
I want to see Exeter and the Southwest UK succeed, but this is just ridiculous.
2018: DRW-PER-HKG-ICN-MEL-AVV-BNE-OOL-SYD-YYZ-YYZ-YUL-YVR-PDX-SEA-SFO-PEK-KIX-CDG-IST-NRT-HND-BKK-FAT; AC J-TK J-OZ F-DL F-TG J/F-NH J/F-CX J-VA J