One of the biggest pain points users currently have is handling environment variables. We're aiming to solve this through this RFC: github.com/zeit/next.js/discussions/11106
Overall we're working on many developer experience improvements right now and solving some more complicated patterns. One example of this is that "paths in tsconfig.json and jsconfig.json is going to be supported very soon: github.com/zeit/next.js/pull/11293
Another thing that we're working on is even more documentation and example resources about general concepts in Next.js.
Overall we closely monitor the Next.js community and talk with users of Next.js both large and small. This goes from Alexa top 100 sites to people building the website for their local bakery. This provides a lot of context into how we can improve the framework.
Most of the features introduced in the past 2 years have been based on feedback from companies building Next.js applications.