I believe that Boeing once proposed something similar based on a 747 with an internal weapons bay, not sure about the refueling aspect.
Fonsini, don't know if it's what you're thinking of, but back in the early 1980s, Boeing proposed a 747 cruise missile launcher. It was basically a 747-200F, with the cockpit isolated from the cargo bay such that they could depressurize the main deck while keeping the flight deck pressurized. There would be a large cargo door that could be opened in flight, and a bunch of rotary cruise missile launchers would rotate around the cargo bay - spitting out ~10 cruise missiles per launcher before rotating the next rotary launcher into position (120 missiles per 747 IIRC). The idea was to have a fleet of these 747 missile launchers that could loiter outside Soviet air defense range, then launch several thousand cruise missiles in minutes, overwhelming the Soviet air defenses.
The KC-46 has a whole lot of bumps and blisters unrelated to the aerial refueling task - presumably they incorporate self defense measures of some sort (I know a bit about that part but can't talk about it for obvious reasons).
My first thought regarding a stealth KC-? is they'd be looking at ~$20 billion development program before they ever produced a production tanker. That's a whole lot of money for some very questionable benefit (serious question, has a USAF or NATO tanker ever been successfully attacked while performing an aerial refueling mission?)