This may seem like a pointless comment, but I personally feel that it might be worth bringing up...but how relevant to determining the factors behind which airlines would be feasable at Coventry, would the booking and information systems be for each airline?
I.e. Both Wizzair and Thomsonfly use Navitaire, as do Aer Arran, and Ryanair (however I personally cannot see Ryanair returning to Coventry) who have both also been mooted as being potential airlines for Coventry. Easyjet also use a system closely linked to Navitaire...again very unlikely that they would come to Coventry.
My theory is that Coventry is very much seen as a low cost airport and indeed does sell itself to the airlines as such...low cost for the airlines. Therefore, if say Jet2 were to come in using the AirKiosk service, a lot of employees at CVT would need to be taught how to use 2 systems...potential for asking for higher wages...which would in part be subsidised I'd imagine by asking for higher fees for the airlines. However, if by sticking to just Navitaire airlines, then life is a lot easier.
Like I say, feel free to shoot me down...just a small theory I had.