Wonderful sentiment...
The idea at least of a lighter local rail link to the towns to the east using in part a non airport historic layout from decades ago has been resurrected from time to time & I believe the original airport re-development plans in the eighties showed the rail link from/to London being branched from the Braintree line not from the Cambridge line as exists today.
The whole area would benefit with many airport employees residing to the east too.
Sections of the track in the airport`s vicinity became footpaths & I have no doubt other sections have now being built over.
But with this infrastructure deficit Government we must expect nothing to change unfortunately.