What we know as Ultra Instinct reminds me of the so-called "flow state", a state of being where you're one with what you're doing. It's also characterized as being without thoughts; your body acts on its own. It can happen in all sorts of activities, from cleaning the floor to fighting a boxing match.
In Dragon Ball, it seems to me that Goku could already enter this state after training with Kami. He had a lot more maturity and he had learned to keep his mind still, while still being the character we all know. That's what training with a deity ought to do. Even before that, Goku had keen senses. His major weakness was his emotions getting the better of him.
Then DBS comes along and turns him into an idiot, a perfect excuse for a new "form" to turn him into a stoic, but boring fighting genius.
Ultra Instinct avant la lettre
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