At the end of the series, it's revealed that Neva's power boost wasn't what unlocked Super Saiyan 4 for Goku. Goku had, in fact, already reached SSJ4 after the Buu Saga. He just never thought he ...

SSJ4 Goku remains in his child-like “Mini” body in DAIMA. Mini Super Sayain 4 Goku is a design that takes itself a bit less seriously than Dragon Ball GT 's version, and that's ultimately for ...

Goku reaches his limits and unlocks SSJ4 power without magic or tail in Episode 19. Dragon Ball Daima will conclude with Episode 20 airing on February 28, no sequel planned.

So, looking at the SSJ4 transformation, it seems that Neva's magic has two parts. The first is awakening something inside Goku. The second is to create a tail from nothing.