An F-35 sim would definetly be a great one without a doubt. The only problems are resources, since we don't even know what speed it can go. Another problem is simply that it might be too easy, unless we make it difficult on ourselves on purpose or bring the Georgian theater to 2020 or so (when the T-50/J-20 will be out).
On the upside, name something the F-35 CAN'T do. It does ground attack, strike, CAP, CAS, maybe not interception, but mostly everything. There are CTOL, V/STOL, and Carrier versions, as well as the CF-35 which will have a drag chute for icy runways. If you want diversity, look no further.