Hear me out- Reboot with Sam and Dean plucked from heaven to return to different timelines that are in danger due to supernatural events that could alter the future.. Heaven could recreate the bunker they could return too as a base to read up on lore and They can go to different timelines each season Egypt, The dark ages, 1800s, back to the old west, ancient China, the Aztecs, the Vikings....and since its going.through timeliness they could interact with older characters like the original vampire, Crowley, and Rowena.