No reason it couldn't have a entry position and a max cargo position that moves up further. Though I wouldn't expect such a thing until demonstrated.
Actually, they could have put sensors in the back of the front seats similar to what they have in the doors, then have it automatically move forward until out of room based on front seat positions and if there are child seats in the 2nd row. That would be pretty awesome. I think it would make a lot of sense, eliminate certain squish concerns, keep the controls simple and the operation smart, very Tesla-like. If they don't already do this, I think they should. Maybe I should suggest it to Tesla, if not already the case.
