I really can't see it being a heavy rail link but just a fixed replacement for the shuttle bus using the shortest route possible with rope hauled trains on rubber tyres.
http://www.dcc.at/solutions/technology/ With an interchange on the northern edge of easyjets HQ the walk would be around 75m to the new terminal entrance.
As for continued easyjet aircraft maintenance at Luton the jury is still out as to whether Signature will in the long term want to keep Landmarks hangar, which used to belong to Monarch, or even their new hangar by cargo so keeping the Landmark hangar. Worth remembering that Signature has a history of building a hangar and then leasing it out, which is what they did with the hangar Gulfsteam now occupies.