The prequel battle droids not looking like IG-88 was a missed opportunity.
This is a ultra-fantastic idea. Why didn’t they do that!? That would have made so much sense… IG88 being a leftover droid.
The Clone Wars CG animated series had these droids in several episodes as well, mostly portraying them as specialized for assassination, so that is probably the direction canon is leaning now. Even so, a retcon that even just has specialized IG88 assassination legions (terror/kill squads) would not only be plausible, but a strong idea.
Ideally someone gets some IG88 Maya models or something and recomposites droid battle scenes from the prequels to feature a few or even all IG88s -_^