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From what we have gleamed from the few tib-bits of information given out on Behaviour Interactive behalf we can assume that we can expect the stereotypical shadowed variants of CSM classes like raptors to assault marines, chaos terminators to terminators havocs to devastators etc. But what about the apothecary?
Sorcerers could be a possible candidate although from a lore perspective sorcerers tend to be greatly distrustful to CSMs in general especially since most of the time they tend to look out for their own agenda rather than that of the legions or hosts Warlord. And I can only imagine them being the more of the blasting and cursing of sorts than one to look out for the general well fair of the war bands fighting capabilities. I'm sure if the story is clever Nurgle devoted sorcerers or of that nature can be forced or pacted to work with the other CSM legions though it'd have to be a fairly strong or binding pact/agreement.
Another possibility could be genetic possessed flesh crafters who could meld the flesh of the CSM and inject them with a series of potent drugs and adrenalins fuelled by foul demonic alchemy and sciences, though they are very loosely mentioned CSM variant and are only plentiful in war bands who pay particular homage to Slaanesh so again there would need to be strong lore binding reasons for them to stick their necks out for this particular crusade.
Then there's the possibility of dark apostles from the Word Bearers Legion. I'd admit they aren't exactly the most plentiful of CSM variants but they are perfect to fit the bill of on the field support roles. They spout sermons of dark faith in the name of their dark gods perform ritual sacrifice and on occasion summon and control small hordes of daemons. Once more this particular special units presence on this crusade would have to be explained. Perhaps the Word Bears have a stake in this Crusade and fear that the CSM legions have a stagnated leadership and feel the need to have many apostles fielded to ensure that their purpose and cause are not forgetten...as well as to further the Word Bearers own ends.
But anyway much of what I've gleamed of Chaos is from the codex's and novels provided in my short life span of 20yrs so forgive me if I've left anything major out or haven't detailed more in certain favourable aspects.