Is this possible natively since iPad has USB C?
There is Luna Display, which plugs into USB C or MiniDisplayport to pretend to be a monitor. Then it routes that image either through USB(lightning) or Wifi to your iPad.
I have luna as well and it's pretty good as a second monitor but if that's your daily setup especially with an expensive computer like Mac mini I feel sorry for you. There's a noticeable delay, as in the mouse cursor feels floaty, videos will skip frames and sound will come a bit faster than video and image quality is comparable to airplay, it's compressed.
I don't think you quite understand it. Just how you can't plug in a Mac Pro into a MacBook to output video, Usb c is the same. It only transfers video one way. Our only hope is that usb c improves data transfer speeds then that would allow faster and better incoded video transmission. But quality wise that still wouldn't get it anywhere close to even a $100 display which is what I'd recommend you getting.Oh yeah, well maybe it will work with the new iPads directly as it's USB-C now, as iPad to Monitor works. I don't think it would be much for Luna or another company to make an app that makes the iPad act as a monitor via USB-C, then there will be 0 lag.