I agree, it's run its course, not in a bad way, but I think they're out of runway to go any further. If you think about it, it's had a lot more plot in 4 seasons than most of Shur's prior sitcoms had over their longer runs, and extending it with more "memory reboots" would have felt really cheap. I think it will be interesting to see how much impact the super serialized style has on sitcoms going forward. As much as I loved this show I still like the less demanding balance of something like Parks & Rec still feels more comfortable.