The target thickness really needs to be under 13mm, if they can get it close to 12mm it'll be a big improvement.
Looking at the leaks, it actually looks like they've gone from the Speedmaster Pro case shape that the original Planet Ocean was based on, to something like the FOIS case, but with crown guards. Definitely an interesting approach but if that plus the solid casebook and presumably a Cal 8806 movement can bring the down into that range, it could make for a very nice watch on the wrist.
It'll make the thicker PO 39.5, which is currently the best PO in the lineup need an update too though as it'll be smaller but fatter by comparison.