Nioh’s a game that went through a ton of iterations that never went public—it’s very loosely based on an old unfinished Kurosawa script that the president of Koei had some weird fascination with, and so he simply would not let it die and would make different teams restart the project whenever it looked like it wasn’t going anywhere. It was allegedly an RPG, a musou-style game, a dungeon crawler, etc and even once it was given to Team Ninja, it was drastically reworked a couple times to make it less Ninja Gaiden-y. That game was announced for PS3 in 2004, well before the PS3 was even out, and didn’t hit the market until 2017, and I can’t think of any other games that were stagnant for so long that ended up being anything more than an interesting footnote.
HAL’s Kirby game for Wii is also interesting inasmuch as it was the first HAL-developed console Kirby game in over a decade (Air Ride aside)—the previous one came out for N64, with multiple scrapped games in between, and they’ve talked in vague terms about the incredible hardships they faced with every cancelled project without ever actually explaining how they managed to somehow forget how to make Kirby games (especially given that they were cranking them out on handhelds). I guess losing Sakurai and Iwata hurt them more than one might have presumed it would.