The classic space age SMG! Went into service in 1990, but development was started in 1986, so by 1989, it’s not outlandish to think that FN either rushed to complete development, given the new robot threat, or even just pushed a prototype to limited production to help in the fight.
I think the spaceage looks would make it fit right in for fighting robots!
I think the lore is that arms and supplies were dropped by allies after the initial uprising. Since NATO is one of those, and the P90 was originally a NATO design contract, I feel like it all works.
If they didn’t want to broach the 9x19/9x39 thing again, I’d be okay with them making a slightly fictional version that’s chambered in 5.56mm rather than 5.7mm…although a faithful representation of the 5.7 would be well suited to anti-robot operations I think. A little bullet, but blazing fast.