I am tempted to steal the idea for Honorguard Counts as Grey Knights. For one, I do love my Smurfs and the fluff associated with them. I also LOVE the idea of not having to spend a crap ton of money on stuff like Dreadnoughts, Rhinos, and Razorbacks. And if I do it right, it would be a nice way to "be different" from the rest of the bandwagon jumpers. I could kit bash the hell out of the GK, Sang Guard, and other kits and get some Roman-style crests for all the helmets.
A lot of the rules and gear can fit an Honorguard/Vet force pretty well, but there are quite a few "stretches" that might cause problems. The pysker and demon rules would not have any real justification besides the "rule of cool". Here's what I'm thinking:
GKTs/Paladins = TDA Honorguard (creative, right?)
GKSS = PA Honorguard
Purifiers = Tyrannic War Vets (I thought the "FU Gaunts!" ability was appropriate)
GKGM = Captain
GK Libby = Libby (easy enough)
Dreadknight 1 = Papa Smurf
Other DKs = ???? (I want to use multiple DKs)
Interceptors = Vanguard Vets (would probably use piece Sang Guard Models)
Inquisitors = PDF leaders (TDA one would be hard to justify)
Warrior Henchmen (probably won't use) = Ultramar PDF or Scouts
Pyscannons = Assault Cannons
I'm not sure if I will actually go with this, but it's definately an idea I will be thinking about this week.