House Rule I've been considering. Constitution gives a minor bonus to Endurance, which affects both the number of hits someone can take and how long they can withstand bleeding; it also gives a decent bonus to Stamina RR, which helps resist Stun. But considering the relative unimportance of Concussion Hits in combat, compared to Criticals, it seems like Constitution has far less to do with character survivability that it ought.
There are a lot of games that use an attribute like Constitution to reduce damage, instead of providing a bonus to HP. (Or both, like the new Shadowrun.) So, I have been thinking that perhaps 2 x Constitution Bonus could be added to DB alongside 2 x Quickness, to represent thicker bones and heavier muscles deflecting cuts and absorbing impact, in much the same fashion as the Dense Musculature talent.
As a side benefit, this would replace the Large and Huge critical charts, since Large and Huge creatures typically have much higher Constitution than they do Quickness. This would keep Attack types more consistent, and allow the differences between them to still be reflected in combat against these larger foes.