There are plenty of successful mods and even paid products capable of making a MacBook include a functional touchscreen.
As far as I know the closest thing you can do with an iPad running macOS is some form of Remote Desktop / VNC. The QEMU attempts on jailbroken iPads are unusable, and impractical. Certainly no one has done it natively (outside of Apple of course)
I want a Mac with a touchscreen and a pencil. So not sure if it's easier to retrofit MacOS on an iPad or retrofit a touch screen on a Mac.
I know this question is adjacently relevant, but I wonder if someone has some experience in it and are willing to share :)