While researching on the development of Majora's Mask I found something really interesting…
"Koizumi: Actually, at the time I started working on Majora’s Mask, I had already been busy designing another game. I’m incredibly ambitious, you see. But then, Miyamoto…
Miyamoto: Recalled you.
Koizumi: I heard the whispers… “Zelda… Zelda… Zelda…!” And my game was canned!"
Source: www dot glitterberri dot com/majoras-mask/staff-interview/zelda-is-always-bringing-something-new-to-the-table/
So between Ocarina of Time (late 1998) and Majora's Mask (early 1999) Koizumi was working on another project! That really blew my mind. Also, it appears that OoT and MM cutscene director Takumi Kawagoe worked with Koizumi on the canned game.
I'm really wondering what Koizumi's canned project could have been. Maybe this was Super Mario 64 2? After all, this was canned around 1999, for all we now, and both Koizumi and Kawagoe worked on the original SM64. But then comes the following passage:
"I’d originally been designing a board game, based around the theme of cops and robbers. I wanted to make it so that you technically had to catch the criminal within a week, but, in reality, you could finish the game in an hour. I figured I’d just throw what I already had into Majora’s Mask."
Seems like Koizumi had a more original game in mind. If I understand this correctly, he transfered the time concept of his idea to the Majora's Mask project, after his own game got scrapped.
Maybe you have an idea what game Koizumi could have been working on? Is there more information? I'm really interested in this one!