If ther is some doubt about what aircraft should have ben developed for the late war day fighter, there should be little doubt about the choice needed for the night fighter. The Ki-46 would have made a twin engined night fighter as good as the Mosquito, less the radar. if the japanese could or obtained a design for a workable AI or passive detection system, they would have reduced their losses to bombing in the final year of the war considerably, or alternatively, increased the allied losses. B-29 incendiary raids, which did the lions share of the damage to Japanese cities were undertaken at night, at relatively low altitude. A coherent, properly trained and proportioned night fighter force might have reduced thosde effects.
The historical conversions were designated Ki-46 III Kai, and were not that successful. The engines were of too low a power rating to achive a sufficient climb rate, the basic airframe too lightly built to allow violent aerobatics, and the control surfaces too small to give the type much manouverability. However, what was needed was the fitting of a higher rated engine with better high altitude performance. This was available in the Ha 112 itself rather problematic but an engine with great potential IMO. Work needed to be undertaken to improve the serviceability of this engine, and to increase production, but none of this was out of the question.....it just needed better access to resources and production space. Once the engine issue was solved, changes could have been made to the airframe that would have made it a 1st class night fighter. The Ki46IV prtotype was heading in that direction, but the shortage and poor reliability of the Ha112 engines basically killed off the whole project.