Next seems to do a lot right. But there are some big gaps that they need to fill to be the canonical SSR framework.

For example getInitialProps being isomorphic means there is no good way to define controller-like behaviour (redirects, error codes, data fetching). Their examples literally tell you to have the function check whether you're executing on the server or client and have the implement the desire to behaviour for both environments.

Their new APIs seems to be pushing people towards building functions for data loading that are deployed as standalone lambdas. This is not nearly as elegant as the solution they have for pages (any thing stored as "pages/:name.js" is renderable).