Yes, that is what I was thinking, a sapphire would be gorgeous.
I found a pink paraiba tourmaline that would be gorgeous in that, but it's too big. Not sure you even like pink, lol, but I was considering an alternative to the sapphire I'm getting, because...I don't know, just cuz, lol. 8.5 in a cushion shape is a nice size in a diamond, or light stone. It'll look great, whatever you do.
Oh and I suggest sticking with a calibrated size, like an 8.5 vs 8.6-8.7 to make a switcheroo easy later on when the AVC come available.
Unless, of course, you don't want to alter it now, but rather later on to make sure it fits the Amora perfectly. Remember, Kanga's Amora OEC didn't come exactly at 8mm...