The best I can speak to the center position is that a normal sized adult will not have nearly enough headroom. And you may know that Jeff was unable to on either outboard position without his head against the headliner. He'd need another 1.5" of space to clear it.
In the center position, there's enough "arch" to the padding that a rear facing child seat might never sit flat and secure enough that you'd confident that there would be significant "rocking" from side to side.
I'm not trying to paint a bad picture, but putting your weight on to the child seat enough to really push it down and get that belt tight (if you could even maneuver in to do it) could be a real challenge. And it appears the child seat might not clear the front seatbacks.
For sure you'd need a seat protector so the rough edges of the child seat base don't destroy the seating surface.