So dump the airframe and retro fit the new information systems in to the existing F-15E and get 3 times as many for the same cost?
Wab
The silent eagle would have approx the RCS of a superhornet (maybe slightly less due to internal weapons capability of the new conformal weapons bays) but would have a significantly greater payload, range, endurance than then F-35. Downsides are long-term expense... Second engine and seat of the F-15E would be a continuing expense. Cost savings development into whatever engine would be put into a new-build silent eagle and increased integration in the aircraft avionics and systems might help mitigagte the cost, but the development costs would not be small and per-aircraft price would be high. The main savings up front would be not having to start up a training program from scratch... Existing training systems could be adapted and cross-training from one F-15 variant to another has been fairly straightforward in the past.
But the USAF is under a SECDEF and SECAF directive to not purchase any non-stealthy manned combat aircraft, so it probably won't happen.
On a different note, Secretary Gates indicated that he wants to talk to Japan about a suitable policy regarding China's J-20, after it demonstrated its first flight. As a wild guess, that sounds like we'll either re-attempt an F-22 sale to Japan (unlikely IMHO) or attempt to sell them something sooner than the F-35, possibly new-build air defense F-15s, taking advantage of all the latest developments for that airframe. A full-up AESA radar with the best digital signal processing, better RWR and internal jammer, internal weapons carriage, and new engines offering high mach supercruise, would make for one hell of an effective air superiority fighter for Japan. Add better pylons (or activate stations 1 & 8 under the wings) and the plane could carry 10 AMRAAMs for cruise missile defense or defense against escorted strike aircraft. The silent eagle treatments might even make this a survivable mission by shortening the effective engagement range against the F-15.