All existing masters go Arcanists except Ironsides & Mei Feng; newly arrived Hoffman logistically goes M&SU to balance things better, but thematically I enjoy the idea of him working with the terrorists and against the terrorists at the same time.
I say leave Marcus Arcanists/Neverborn for now. Might go full Neverborn in 4th edition.
Ivan can't be with Mei Feng yet, and bridging them across 2 factions, both alike in dignity, in fair Malifaux where we lay our scene, would be dope.
This would unfortunately make Frontier just Guild, but Wastral Ten Thunders/Arcanists.
With the current story climate, I can see the Freiholt story going differently and Freikorps becoming Outcast/M&SU as a more militant protector of the people, as a giant middle finger to the Governor-General.
If Apex came in still....no, Apex cannot come in here. It doesn't not fit any of these factions in this climate.
With this weird direction and focus on magic in the Arcanists splinter cell, I could see Transmortis starting there instead of Ressers.
M&SU needs a charismatic street preacher. An Obey master, who turns scheme markers into mobs of Malifaux Citizens (well call them Mob Tokens) who cause all models to be slowed around them, hampering activity as more and more Mobs of people clutter the table/town causing trouble for everyone, but members of this keyword, let's call them Shepards, can bonus action push Mob Markers around as they lead their flock from hot spot to hot spot. (i just stream of consciousnessed this, hopefully it sounds good)
Then M&SU gets a street gang of protectors, like the Champions of New York, looking out for the every day citizen. Just a crew of weak to mediocre models where everything is Plentiful 5 or more. No summoning, no replacing, just a horde of about 20 models none of which is Insignificant because every man can make a difference!