I know its been expressed and suggestion literally everywhere but character customization much down the development line for non-story, survival sandbox playthrough would be nice. Utilize the pre-existing four character voices for generic 'grunts', "oofs" and actions that require sound bytes that can use the already existing voice work would be development and cost effective. Cosmetic options as unlocks for milestones achieved and even (dare I say it) cosmetic micro-transactions (akin to Borderlands 2) would be cool.
I'm also glad to see suggestions here for what is basically character sheet slots that armor would go into so it doesn't take up inventory space.