I don't think they're really thematic with what the original FoM universe was like, but maybe with some MR faction? I just don't see any factions, but the ones outside the law like FOE, Syn, and GOTC using dual weapons though and that might end up being a balancing issue.
Admittedly, it would look awesome in-game, but I'm pretty sure it would be absolutely horrid to balance out. At this point, we're not permanently ruling it out, but it's not something we're looking to implement any time soon.
How are you going to effectively load twin pistols or anything like that effectively during a combat situation. There's also the problem of aiming, you can't really sight two weapons at the same time.
It would look cool running through a colony brandishing dual-wielding but it just wont be really viable with for example 9 bullets per gun and no aiming vs the clip of an assault rifle you can aim down.