This is BS

There's not an ounce of anything factual on this page or anything that supports that there was ever going to be a Pokemon RPG for the 64DD. Pocket Monsters 64 was a working title for what would become the Pokemon Stadium expansion that we received in the US as Pokemon Stadium 1. It was never going to be an RPG, and Miyamoto never said it was going to be.

The "June 1997" EGM is available on archive.org and there's no mention of Pokemon in it what-so-ever. The scan of EGM used as evidence on this page is actually from the September 1997 issue, and again, they are talking about Pokemon Stadium. Note that the word RPG is never used in reference to Pocket Monsters 64 even once.

The reference to an archived N64.com listing for the game is also garbage as the page linked here doesn't mention Pokemon either.

I think the misunderstanding came from Miyamoto occasionally bringing up Pokemon as a comparison point when talking about Mother 3 and Mario RPG, which were supposed to be launch titles for the 64DD. Pokemon was brought up because it was an example of a successful RPG game, not because they were making a Pokemon RPG for the system. Additionally people get confused because Pokemon Stadium and Pokemon Snap did get released under different circumstances, but any idea that "Pocket Monsters 64" was ever anything but Stadium 1 is just pulled out of thin air and supported by nothing factual. Bulbapedia even deleted their page for the game because they couldn't verify it.

This is a creepypasta tier rumor and deserves to die.