The only thing remaining to have a complete developer experience on Windows would be to convince Apple to allow building of iOS apps on other operating systems.
Beside that reason (true) a mayor roadblock would be that the iOS simulator (the simulated debug device running alongside Xcode on the development host) is a simulator, not an emulator: it runs iOS libraries re-compiled for x64 using the macOS kernel (and the macOS Foundation and Cocoa libraries) support. Porting that on another host OS is probably borderline impossible. Doing something borderline impossible that will increase your support requests just to make people stop using machines you sell is not a good business proposition, I suppose.
I think it’s never going to happen. It’s the complete antithesis of everything that Apple stands for as a company.