Specifically a Future Variant resembling either MechaMew2 from the live show or Armored Mewtwo from the anime?
It’s just one of those things we’re overdue for imo. Another one being an ice type Onix, as it was the first region variant back in the anime.
Ice Onix wasn’t wearing a hat, and weren’t the giant Pokemon revealed just to be robots.
As for Mecha Mew2, yeeee
Not all the giant pokemon were robots.
The dragonite and tentacruel were real pokemon.