Nobody's really sure why it was cancelled, but it must have happened early in development, as no screenshots have ever been released, and no prototype ever found, much less dumped.
lostlevels has a small thread on the game.
http://forums.lostlevels.org/viewtop...f40de6cf3f8e27
This can be easily compared to other cancelled games I really wanted from that time period, including the NES version of SimCity. Unfortunately, the prototype of that is at Nintendo head office, so there's pretty much zero chance it will ever be dumped.