The engine is similar to the Gen1 Superduke GT which came with the QS as standard, but I have no idea what extra components are required inside the gearbox, or sensors and wiring.
If it was available you would of through KTM would offer it like they do for the newer SA-S and SA-R models where it is just an electronic unlock.
Got the QS on my 1290S and quite like it, I find it more of a labour saving device than anything else, certainly a feature I can take or leave personally and with 3 other bikes I never ride one of the others and wish it had the QS, but I do wish they all had Cruise Control!