I'm only familiar with Bloodlines 1 so all my ideas come from there.
Could maybe make a game where you run a black market out of the back of a van like Fat Larry. Or a murder mystery game where you as the Malkavian detective have to talk to the objects in the crime scene to solve the case. Or maybe a haunted house experience similar to Ocean House Hotel.
I am looking to join a team but if I end up going solo I'll probably do the haunted house idea since it'll likely require the least amount of code to get working, letting me focus on the assets instead.