I see a Commissar based in Guardsman as the bolt pistol, whip toting hardliner pushing a penal platoon into storming a heavily defended fortification. Gaunt, from Gaunt's Ghosts, would be very well represented by a Cleric build, Hark would fit as an Arbities and Ludd would fit as an Adept or Cleric.
The Adept and Cleric both make good IG officers with very different strengths. One is the high command tactician, the other is the charismatic field commander.
Black Industries with the IHB added a lot in the way of background packages and alternate ranks. I did not mean to imply that BI didn't see the flexibility in the system they designed, they just led the way for FFG to really push the idea in the RH and BoM. When you take a look at what has been done in RT with ItS and DW, with what we are hearing about RoB, you really start to see how flexible the career path actually is, and how important these extras are in fleshing things out.