Idk about a whole new system just to force the player to complete mundane shopping lists for lube after every excursion.
But you're right that sex and battle is too easy. Being on the receiving end of submissive sex could include damage, or getting pumped too full (ettin) could be small damage over time. Good ideas. A better fit for developers would be to change enemy AI so that they try to dominate you and keep you pinned down or impaled on their cock until you submit or faint.