Like inferno or preact.

From the end user perspective, it would work as follows.
Configure package.json:

{
  "dependencies:" {
    "next": "x.y.z",
    "next-preact": "x.y.z",
    "preact": "x.y.z"
  }
}

Then we transform JSX to the pragma that, in this example, next-preact would need.
The rendering pipeline would similarly be pluggable.