From my understanding, the OTP framework designs gen_server (called GenServer in Elixir) to act as both a server and a client, similar to the TCP server/client pattern. It maintains state, but developers need to handle persistence themselves if they want to restore the state after a crash. It also receives configuration/options from a supervisor (or via manual start) and initializes its state in the init callback.
I think this can be annoying for developers when handling state in some cases.
In my opinion, a GenServer with a pluggable architecture, similar to Phoenix, would be more flexible and better aligned with the Elixir style.
Another interesting component is gen_statem. It is quite suitable for working with state transitions. I saw that Elixir implemented it in the early days, but it seems to have been discontinued.
For DGen, at first glance, it looks like a remote GenServer running on another node. If the goal is to share or persist state, this could be achieved by adding an adapter layer (similar to Plug). I think this would help users support more use cases, such as storing data in Redis, Postgres, etc.
