I would like a 5"-barreled Match Target SIG P229R with a solid stainless steel frame and the DAK trigger system, with both .357 SIG and .40 S&W barrels fitted, tuned for robust reliability more so than accuracy. Rear sight? Bo-Mar or equivalent. Plus, a normal-dimension spare upper unit chambered in .40 S&W, so I could qual with it annually as a duty pistol. While I am a sixgunner at heart, this would be a back-up pistol for big-city police patrol. Not concealed back-up, but a longer-range fighting pistol for the "war" bag, that would share magazines with the P229 in the duty rig. A pistol for a nightmare scenario along the lines of Columbine, North Hollywood, Virginia Tech, that would continue to be a recreational tool after I retire.
SIG did market a P229 Sport, which is not far from the above ideal, but its longer upper unit was chambered for .357 SIG, at least in the examples I have seen. I need .40 for magazine interchangeability at work.
SIG does market a 5" Match Target P220, but it is in .45 ACP, and if I recall correctly, not available with the DAK action.
SIG also markets X-5 variants of the P226, which could possibly be extensively modified to work with P229 magazines, but they seem to be highly tuned and finicky target pistols; I want robust reliability, like a stock pistol.
Assuming this will not happen before I retire, it is more likely that I will have a custom 'smith like Alan Harton build me a custom single action sixgun based on something like a USFA Single Action. Exact specs to be determined later.