I'm trying to create a good fluffy army for friendly play (tournaments is something else of course) and thinking about what defines the Mordian army. I'll have to read the fluff in the new codex but I'll have to use the old doctrines as a start. Ratlings are of course in, as are Psykers (bringing along a Psyker squad to go with the Ratlings, but not sure about the Primaris). Heavy weapons platoons aren't in, although I could just take more heavy weapons squads; I never took these platoons anyways. Diehards I never took, but Commissars for my combined infantry platoon is a must. Sharpshooters will be represented by orders, nothing too special there. Not sure if I'll stay away from the formerly prohibited units; they could be prohibited on purpose, or just weren't worth the doctrine choice (although Cadians got 7, along with possibly another regiment).
I also want to conform to a more militaristic guideline, follow how a company would actually fight. HQ squad (maybe with a second company command squad for a 2IC), and a couple infantry platoons to start, and then take support in squadrons if possible.