One request would be an official state management extension – coming from Vue and Vuex, this is something I miss. We're currently using Redux Toolkit, but would be great to have something official for Next along the lines of Vuex, Reframe, or Elm.
* update (writing this between lots of meetings :| )
One huge value we get from Next is the opinions and conventions. Large dev teams benefit from this – which is why we've been using Ember and Ember Data for years, and Rails before that.
Having an opinionated state management that plays nicely with Next on the client AND the server is what I'd like to see. We're doing quite a few workarounds currently with Redux to support managing state from within the components and during `getServerSideProps`. If all my dreams came true, it would be nice to persist state conditionally in Redis or Mongo.
Sorry for the rambling thoughts – just loving Next, and incredibly busy building our new core IP with it.