Well, the first thing it would offer, and by far the most important, would be the same moddability that SF enjoys. In fact, my concept is that the SF engine would be used, but with new DLLs necessary to support whatever new features are added. That way, you could add any SF/WOV/WOE planes to the new sim, albeit at a lower fidelity than the F-4 or whatever the study plane turned out to be. Modders could make their own high-fidelity planes if they were so inclined (Mirage Factory).
I think it would offer other things over Lock-On as well. Nostalgia, for sure. But also the fact that so many countries have or still fly the F-4, it should have a lot of appeal throughout the world.
Finally, no one has found the magical combination of fun, playability, and realism that I personally would consider optimal. SF and its brothers are a little too light, Falcon is way too heavy. Lock-On...it never grabbed me enough to delve into it and find out. Plus I don't trust Russians to accurately model US aircraft.