The latest update from Next.js [1] seems to cover all that redwoodjs does. In particular, the Static Site Generation portion. Next.js already supports API's in the same monorepo.
Next is limited to browsers and doesn't prescribe how you access data. I would compare redwood to meteor.js but not next.js.
Is Redwood _not_ limited to browsers?
Correct. One API. But chose the client (or as many) that you want.
Like David said, we currently only help you build a web frontend, but we intend to eventually make it super nice to build a mobile app, desktop client, CLI, etc. All under the redwood umbrella (canopy?).
KISS / Single responsibility
The difference is that Next.js is very unopinionated. GraphQL, Prisma, SQL – these are opinionated choices from Redwood and largely the point of the framework.