So for the cost of the 4" APO one can make a 8" Schupmann and have much better optical performance and more money left in your wallet.
Which begs the question: Why aren't these being made / sold? I got my AT102ED for $600. If an 8" sold for close to that, I'd buy & try it. I don't see anything in the schematics that look like they exceed Chinese fabrication abilities -- but maybe I missed something.