I had a brief stint of working with Elixir a while ago, and got side-tracked and spent that time going down the GraphQL/Relay rabbit hole instead. During that time I was ramping up to help out on the GraphQL Elixir project [1]. I don't know its current state, but it might be worth looking into vs Absinthe (which I'm pretty sure was branched off that project originally).
EDIT: Looks like the repo is pretty abandoned actually, scratch that!