I don't recall seeing an iPad case quite like the Sketchbook iPad Pro case from Longo case. The Chinese company is raising funds on Kickstarter to bring the case to production. It has wire bindings for the cover to resemble a paper sketchbook, and it features a holder for Apple Pencil. It also has two stand modes, one for portrait and one for landscape viewing. The campaign just launched, and as of this writing, there are plenty of funding levels at £18/US$26 that will get you one of these cases for iPad Pro.
Check It Out: Sketchbook for iPad Pro on Indiegogo, a Wire-Bound Case Like a Sketchbook