That WIP scene is hacked in which pretty much confirms he is drip feeding content so that he can milk his Ci-En as long as he can. On the other hand, if he keeps adding to the WIP, then its not so bad as long as you can keep hacking it in.
Simpler explanation would be that he's working slower than his artists. Art is done but stage, backgrounds, sprites, scripting or whatever else is not ready. Files are just in game folder and all this "hacking" does is putting those animation into existing stages. They are not even encrypted - you can simply split them and export as animation within 5 minutes with your image editing software...
Dev is known to be a lazy bum and few years ago it he often liked to "disappear" for months and not post any updates.
Also, Fairy Princess is being developed way faster than any other of his games. We used to get 1 enemy with 1 sprite animation
or 1 CG animation per month. So I guess his Ci-En backers should be satisfied (hopefully this will continue and he won't disappear again).
I'm not defending him because he basically makes the same game over and over (tbh, Fairy Princess has a lot of new things - that probably should be already in Fairy Heart or Flower) and he's slow AF but to say he's keeping the content back so he can milk his supporters - it's probably too much.
TL;DR: He's been milking them for years, it's nothing new and it used to be worse. Now his artists work faster than him and that's why can see new stuff before it's added into the game. He probably should make separate demos for supporters (without unused assets) but he's too lazy so he's just sharing his dev versions...