Personally, given the omnimech-heavy nature of their Coyote allies and the Society's high-tech nature, I would have assumed that the Society fielded old-school Golden Century/Coyote omnimechs, like the Coyotl, Lupus, and Woodsman, before resorting to IICs and SLDF Royals. As omnis, installing Nova CEWS and iATMs would logically have been easier on these designs.
I certainly agree. I was quite honestly surprised that the Coyotl, Lupus and Woodsman didn't appear on the Society RATs (although the Woodsman did appear on the Burrock/Dark Caste RAT). On the other hand, the Cephalus and Osteon appeared more on the Burrock/Dark Caste RAT than they did on the Society RAT, which to me makes no sense. In my view of things, Burrock/Dark Caste RATs should be more likely filled with Royals and other units raided from Brian Caches over the centuries, whereas the Society would use more omnimechs and other high-tech toys fliched from "failed" black projects that were taken off the books.
In universe, putting Nova CEWS on everything should be easy to do, right? I mean, WoB put c3i's on everything under the sun, even old SLDF designs. Of course the Society didn't have the resources that WoB did, so I'm of the opinion that Nova CEWS should mostly be restricted to being mounted on Omnis and other cutting edge forces that aren't meant to be cannon fodder. I really wish that there was a Kingfisher, Gargoyle or Hellion with Nova CEWS. they showed up in the Society RATs, too, after all...
Lastly, yes Nova CEWS + iATMs is a good starting point to give a unit more of a Society feel, but there are other things to consider as well. I would look into using high-tech toys in intelligent or unexpected ways like, improved Heavy Lasers, ER Pulse Lasers, arrays of AP Gauss, mech tasers, mech mortars, Streak LRMs, retractable blades, and heck, maybe even Fluid guns and mine layers. And that's before we start talking about bioweapons, compute viruses, etc. The idea is to throw the (Clan trueborn) enemy off balance with a combination of tactics that synergize and allow the combined-arms Society force to win initiative and overrun the opposing force. When I think of designing a Society unit, I ask myself, "how can I make this unit the just right amount of munchy, that it comes off being munchy with style?"