Though I like the idea of either quality control of material availability affecting what the Ripper is made of, I'd like the Rippers to be Yamataium or Yama-Dura in hull, Zesuaium in blade more. It'd fit with what's happened IC much better and requires less explanation. But this whole thing also made me realize something else.
It looks like the NMX don't have a 'mainline unit'. They seem to go right from Neko Cannon Fodder to Rippers. Yes, they have captured Mindies and Daisies, but by having the word 'Captured' implies that its not in very widespread use. And I'm left a little clueless about the Type 31 and 31 Mishhu. How are those supposed to be used and where? Because there's no clearly defined in-between ground between mooks and the elites, something's gotta get used for something it's not meant to be.
Because of that, I think Rippers are being shoved into the role of 'general purpose enemies'. And for Nepleslian players, judging by the stats on the Wiki, they do happen to come pretty close to equals when comparing a Hostile and Ripper.