Let's get a bit reasonable and serious again and let us ask what the USAF/MoD would gain by using a discarded but still highly secretive X-Plane for throwaway advertisement? Exactly, they'd gain nothing and potentially lose something.
Now let's look at what they'd gain by using some fictional design, of which exist dozens on this forum alone and hundreds on the Internet as a whole. Well, it would be cheaper and easier to use an off the shelf model, no clearance of material required, no potentially sensitive stuff being leaked.
And following that logic, there is little to no reason that whatever anyone uses in commercial material is anywhere close to the final aircraft. At least with Boeings F-47 shenanigans they obscure like 90% of the potential aircraft.