The active stereobase could be a selectable 'percentage' of distance between viewer and currently selected object.
That sounds like a reasonable approach, though it could get very weird when you approach a planet and it seems to grow before you, or when you change selection and the universe crunks to a different scale suddenly.
Still, with some finessing - perhaps a transition of a few seconds between scales, and a cut-off at human scale - I think that would be neat.
I don't think the static human option should be removed, though - sometimes you want to just feel the distance.
Zoom could (and should) be ignored
I don't think Space Engineer meant "zoom" in the optical sense - just as a synonym for "travel".