We share your concern. As I said in my comment above -- the Scala and Dotty teams actively work together (we have our roots in the same research group at EPFL) to make sure Scala 2.x evolves towards Dotty and Dotty evolves towards Scala 2.x. Scala 2.12 and 2.13 will have language flags that unlock features being incubated in Dotty that we can already implement, and the Dotty compiler already has a Scala 2 compatibility mode.

We take continuity very seriously. No one wants a Python 3-style transition. In addition to the desire to avoid this, we also have a type system and a community build (think Google Blaze for Scala) that builds > 1MLoC OSS Scala code.