At the end of the Aftermatch manga, there's an advertisement for REM Racers and the Tohaa pilot is missing from the lineup. This brings me to my next point. Tohaa is in the lore implied to be a One-World government, as such they all move with one purpose, one interest, and that was the hot war against the EI. Now that there's no more hot war the Tohaa has no lore reason to stay in The Human Sphere. This is the issue with a One-World government and drama. They only participate in the drama for the one reason their government has. If Tohaa is to be reintroduced as a playable and supported faction then the purpose and existence of Tohaa need to be reworked. - The criminal organisation that runs everything from behind the shadows needs to go. It's synonymous with the One-World government and their reason is the government's reason. - The government needs to splinter into many separate factions to allow for a diversity of reasons for people to act. This can be made from the existing lore. A One-World government is a tribalistic force where everyone unifies against an outside threat. With the EI having access to a Digester now it has no reason to go after the Tohaa anymore. Without an outside threat, the unity of the One-World government would splinter within a month as separate factions within the unified whole suddenly started vying for their own interests. - Multiple factions within the faction would also allow capitalistic interests to come to the surface. Tohaa is unrivaled in the area of biotech, they're probably even better at biotech than Haqqislam. This would make The Human Sphere a new market for these individual sub-factions to try and enter. It would also place them in direct conflict with Haqqislam since the Tohaa are directly intruding on its turf. Individual PanO companies would be interested in what Tohaa has due to capitalism. Yu Jing would be interested in the Tohaa for the simple reason that PanO is. Aleph would look at them with distrust since it's an unknown force. O-12 would reinforce Aleph. CA has a lot of bad blood with Tohaa, that's reason enough. The Tohaa has been on Dawn at some point and might even be responsible for the Antipodes. Looking to clean up their presence there would bring them to Dawn. The cosmetics part of the biotech would bring the Tohaa into conflict with Bakunin and thus the Nomads. There are plenty of ways that Tohaa could be integrated into The Human Sphere now that the hot war has become cold. It just requires that the Tohaa civilisation suffers from a massive upset in which all the pieces for that to happen are there. As for those companies having military forces. The Tohaa One-World government splintered and a lot of soldiers left the army since there was no direct conflict with the CA anymore. As such, there was a load of unemployed soldiers that only really had a particular skill set and the companies swooped in and scoped them up and are now employing them as their private security. This could also tie in with Sectorials being a specialised force within a company. Then later a diplomatic force could be introduced that came from the Tohaa homeworld and was sent there by their version of the UN that came into existence after the One-World government fell. As I said at the start, with the current lore for The Human Sphere there's no reason for the Tohaa to be there, and with the current lore for Tohaa they only really have one purpose and without that purpose only boring is left of them.
Tohaa is still very much at war with the EI. It is only the Human Sphere that has a temporary peace with the Combined Army. EDIT: In fact, they have even more of a reason to be involved in the Human Sphere as they wish to keep the Combined Army and Human Sphere from coming to a lasting agreement. They want CA to have to keep diverting resources away from the CA/Tohaa War (which Tohaa are losing badly).
I think the reason the Tohaa was left off the advert is purely commercial. The game was initially developed in 2019/2020 when Spiral Corps were still fairly new. However now Tohaa are out of catalogue completely they're not something you're going to include on mass market advertisements. As to the fluff, while the Tohaa Empire is large, you overstate the amount of unity they have. Even on Runohaa the government is split into multiple factions that disagree on policy and direction, just like any government. Each colony also has its own government and bureaucracy with representation in Runohaa, plus the giant ships of the Trident's errant fleet have their own bureaucracies and agendas. The structure isn't massively dissimilar to the USA with each individual colony/state sending representatives to an overarching council/federal government. Then you've got the Trinomial with it's own plans and agendas that often run counter to that of the Triumvirate and Trident. There's a massive amount of politicking and power struggle within the Tohaa Empire as currently written, to the point where diplomatic service is seen as essential as military service within their society. There are multiple ways the Tohaa could be reintroduced to the game already. If they are able to reopen the Daedalus wormhole, or if one of the new wormholes in Concilium connects to Tohaa space, then the Triumvirate would want to defend, or possibly reclaim, the damaged Digester. Victories against the EI elsewhere could allow the Trident to reopen the Human Sphere as a front against the EI, and the Triumvirate could come looking to clean up it's own mess before word of what they did gets out to other Tohaa. If the war against the EI goes badly you could also have a refugee fleet arrive in the Human Sphere seeking sanctuary, unaware of the current cease-fire in effect.
I can see the Tohaa trying to sabotage the fragile peace between the Human Sphere and EI. They'd still very much want the war to stay there than follow them to their home planets. they would sacrifice every living human if it meant a tiny advantage in their war against the CA. If anything, they'd be ramping up their black ops activities.
Certainly the Triumvirate would be, if their agents hadn't become public enemies number one by trying to blow up Concilium Primaris.
