New renderings appeared today, including one which gives a little better look at how the 2nd row seats stow (at least on Sigs):
Thanks, Nigel. Based on this photo, and I'm assuming they've maximized space for the shot, I would guess a max depth of 75" based off of my estimates in the diagram upthread.
And on your attached thread, it shows that the third row seats indeed fold aft and flat, as expected.