What is the most blasphemous human colony you have graced your expanse with. No not basic chaos addled world etc. but something that would really be disturbing for emperor fearing imperials.... like
Tyranidiania(working name)
Ages ago man settlet a death worl, which had a curious property. It had Tyranids but no synapse creatures, so man tamed them. 10k years later planet has 20% psyker population that can act as substitute to a synapse critters. A tame tyranid responds to voice commands quite slowly or inneffectually (like servitor), but beast-master psyker (they have a soul-bond to a planetary host on tyranids) commands them with very good efficiency.
Also military-wise xeno-chitin armor is very common because soldier wearing on can command critters(as tame tyranids are called) more effectively even if not Psyker.
So in this worrld we have hormagaunts as house dogs
["Spot, down, stop harassin our guests...." and hormagaunt drop down like dog. {disturbing is it not for an imperial]] and Carnifexes as cranes and other construction vehicles. Lictors as hunting hounds etc. Technologically this World looks like somewhat early imperial (visual cue Star Craft). And/But their genetic science way ahead of the Mechanicus/Imperium they regularly clone the useful bioforms.
Now a question what would their starships look like??
PS: More blasphemous splinter human societies later, more blaphemous societies. like world of nulles or phoenix pocket empire ( http://seikai.wikia.com/wiki/Humankind_Empire_of_Abh as an idea)
./MP