I am always intrigued by little gaps in a hero's backstory that leave some wiggle room for new story potential, and I wonder if the evil creeps that experimented on him while he was a prisoner experimented on any *other* inmates, and possibly were attempting to create a kind of super-soldier with treatments involving various systems of the body. Anyhow, great concept. I think David Walker touched on that concept on his shortlived series.
Luke's skin and musculature got enhanced, but it could be neat if some other inmate ended up with enhanced nervous system (and basically super-speed / reflexes) or something. Presumably none of these inmates were volunteers, and presumably most were failures (since there haven't been an army of Power Broker'd ex-cons running around... Or have there?), and got disappeared by the experimentors, but also it's quite likely that any other successes (like the enhanced nervous system dude I just proposed) were *not* falsely imprisoned, and actually were a bad, bad person, exactly the sort that would become a super-villain with their new powers!
Or the secret backers of the research kidnap Luke Cage to analyze why the procedure that they've attempted on others since then has only succeeded on him, so far, and if they can isolate the factor and pump out an army of bulletproof super-soldiers...
Basically, his origin story has a lot of potential to mine for future stories. Were the experimenters in any way tied to the Weapon X or Super-Soldier or Power Broker researchers? Probably at least remotely, even if the various head researchers had met at conferences or gone to school together, and quite likely some of their research crossed back and forth, either officially or covertly or via espionage! And so Luke Cage might have some funky ties to folk like Wolverine or Captain America or such icons of the superhero community as D-Man.