As much as I enjoy the IG, I got to wondering about campaigns using Battle Sister and Space Marine squads, especially with the idea that, if you're the advernturous sort of GM, you might have players contolling both an IG character and a parallel Sororitas or Astartes character in a area of the same world, possibly never to meet, possibly not even aiding the other's objective (maybe inadvertantly hindering them!).
I suppose it could also work in a similar fashion if one wanted to do an Arbites squad RP, patrolling the streets, pursuits, raids, riot suppression (possibly in conjunction/coordination with Guard/PDF units), having a catchy theme song when the vid series airs, knowing that they won't be pre-empted by broadcasts of sports. "ARBITES is brought to you by the Pax Imperalis. All suspects are subject to Imperial justice."
I blame this musing on Plushy and Snap_Dragon making conversion threads.