apollo-link-state would almost certainly be considered a hack if it was made by anyone else other than the Apollo team. Just the fact you need to manually specify the __typename field feels wrong to me. But I do have hopes that Apollo will grow and improve here, and apollo-link-state will likely evolve into an elegant tool.
I felt the __typename was really awkward too, but Peggy Rayzis (of the Apollo team) told me awhile ago that they're working on removing that requirement, if it hasn't been done already. I don't think it's anywhere near as feature rich as MobX for local state though, so I use Apollo for remote data and MobX for local.
