Though the jigs are long gone, it would surely seem certain that BAE could sell a reasonable sized batch of new-build Canberras as high altitude recce platforms, radar platforms (with operators 'migrated' to ground stations as the USAF plan to do with the E-3) and for Elint/ECM, etc. They might even carry a Storm Shadow or a recce UAV.......
Such an aircraft would be useful, especially if it was based on the NASA WB-57F airframe, with the PR9's current recce suite as a baseline.
Such an aircraft would offer massive performance advantages over any converted biz jet, and by basing it on an existing airframe development costs could perhaps be reduced to the point where unit cost might be manageable.