When you look at the X-47b UCAV, you aren't looking at an aircraft to engage other aircraft, you are looking at a strike platform that goes downtown and drops a couple JDAM. They still aren't cheap, and you want them back. That still requires a full sized carrier deck.
I would look at a ramjet powered drone, with rocket powered launch. smallish fold out fins, enough to get good g-turn rate at high speed. Electrical power by Ram air turbine and/or chemical batteries. You want it to be fast so your target doesn’t move or hide before you can kill it.
If you want to kill something, your drone starts to look a lot more like ordinance. If you want to loiter and observe, then it looks a lot like a globalhawk or predator.
In a situation where you are not sure, you start off looking and may thus find something you want to kill, you get a UCAS looking equipment, and off load the ordinance function to something it carries.