I'd be happy for a mere port at this point. There are so many cool Mario Maker levels out there that really should be made available to Switch owners. Why Nintendo didn't release a Switch version right after launch is beyond me.
A sequel with an added 3D World mode would be pretty cool.
the answer of why they didn't immediately release a port is probably a couple of reasons. One, you don't want to oversaturate your system with 'Mario' games and help enforce a false (semi popular) narrative that Nintendo only releases colorful platformer games. B, Nintendo wants to spread out their releases. No point in rushing out all of the easy ports to the first 12 or 16 months and then having few easy options later on. And, C, it's highly possible Nintendo will be working on a sequel that employs the Joycons/Switch functionality uniquely. Obviously a direct port of Wii U Mario Maker might be a bit awkward given that it was one of the few Wii U games heavy on employing the Gamepad.
I'm personally hoping for the latter option, a sequel of sorts. Like a 1/2 sequel, Splatoon 2 sort of thing. Not a massively changed game, but just added features and visuals possibly