We (the team at Lightbend) promise to publish something about this before too much longer. The short answer is that 2.13.x pull requests will continue to be merged, security vulnerabilities will be addressed, compatibility with new JVM versions will be ensured, and releases will continue indefinitely, as long into the future as anyone can possibly anticipate, certainly for years to come and almost certainly for a decade or more. There is no plan, and not even any desire, to EOL 2.13 at all.
But yes, we need to arrive at official wording, get the Center’s agreement on it (since if, god forbid, our team or all of Lightbend were to disappear, the Center would have to somehow take over or find a new home for maintenance), and publish it in an official location.
We also need to find a somewhat weaker wording for 2.12. There is currently no plan to EOL 2.12, but it’s plausible to imagine that changing eventually, especially if our current commercial funding earmarked for 2.12 maintenance were to end.
Note that my remarks are limited to Scala 2 itself: the compiler and standard library. As for the library and tooling ecosystem, see fanf’s post.