I think I'll try him in my 29 gallon community in a month or so and see how he does. It's all nano fish save for my two weirdo gobies but I'm not sure if the threadfins and he will get along. Regardless he seems to appreciate being out of his tiny cup!
It is sorta random how you can occasionally find a gem of a betta at Petsmart and Petco. I think the suggestion to check right after they get a new shipment is a good one. I think that's what this must have been, a good half of the bettas on the fish wall looked ill or much older than this guy. He was part of a very healthy looking group on a shelf by themselves, so I think they must have been relatively new to the store.
I'll have to put updated photos of him in a couple of weeks once he's less stressed. I'm curious to see if his color deepens any!