Well, there's always Martin's study of a "flag officer transport" version and the various permutations that could be done with that.
I wonder how an updated one with dry modern military turbofans (F404, F414, RB199, EJ200 - depending on time frame) in place of the dry Avons. It would take some nacelle redesign to accomodate the separate accessory gearbox that modern engines use as well as some juggling of location for weight and balance purposes, but it's doable and you've got a long enough tailpipe that you could add a mixer nozzle and really reduce your exhaust IR signature.