I think the play is that they're going to spend an episode or two setting up either withdrawal symptoms, or more likely, a resumption of the guilt he felt after the war (casualties he caused as a result of using the super soldier serum. Perhaps he even created/isolated it in the first place and is disheartened by the violence it enables?).
I don't think this episode was meant to explore the trauma, but 'teasing' future plotlines about M'Benga's culpability and/or guilt over the stuff. Remember, Chapel reminds him that he hates it and wonders why he keeps some on him, and he responds that while he does hate it , it might come in handy someday.
I think that serum is what gets him demoted. He and/or Chapel are certainly going to use it again in a situation where he can't just omit it from the after-action report. And if it's S31, then he definitely will get in trouble for holding some.
The currently ongoing Star Trek comic book series basically does this.
Sisko (returned from the wormhole) takes a Dirty Dozen style Starfleet team from different eras to handle a mystery. Data, Beverly, Tom Paris, Shaxs (!!), etc.
Also, Worf bands together with Spock, Ro Laren, Lore, and B'Elanna to do another mystery.
Eventually, they team up because clone!Kah'less is up to no good.