Here's just an idea I had (and may attempt to do) while in another thread about penal squads. The idea is that the majority of the army is abhuman or not "regular human" .
HQ
Primaris Psyker
ELITES
Ogryn Squad (5 man)
+chimera
Ratling squad (5 man)
Ratling squad (5 man)
TROOPS
Penal Legion Squad
Penal Legion Squad
Penal Legion Squad
Penal Legion Squad
These penal legion squads would be comprised of abhumans/subhumans like beastmen or other "undesirables".
This comes out to about 750 points. I'd have to add armor and other vehicles (maybe driven by subhumans or humans "convinced" to do so by the HQ) to grow it. This army could represent an all-canon fodder force or some sort of traitor guard formation.
Right now, this is just the start of a concept army, but does it have any potential?