If I recall correctly Perutrabo made a big cleansing operation when he took over his legion, killing 10% of the Iron Warriors. His Legion is possibly the most ruthless of all Chaos legions, even using Daemons as cannon fodder.
I'd like that trait to be represented by their primarch. So maybe some Commissar-like ability, you kill one of your own models and the whole squad can reroll hits and wounds. I know, Guilliman does it without killing, but this is Chaos (and would make perturabo cheaper
).
Some Bonus for vehicles would be nice, he invented the vindicator after all.
Also, he should ride a Maulerfiend.