I really don't think the airport would design its runway to keep certain airlines out. After all, the airport it trying to expand the number of flights not limit them, so if and airline like Ryanair came along, they wouldn't turn their noses up at them, that would be stupid and a large amount of business would be lost out on.
I'm sure the airport built the runway as a long as they could (or to what ever length made financial sense). I also think that the airport won't expand around EasyJet's demands. There is nothing wrong with competition even in a smaller airport!
