* Generally a more clean language for everyday use, codifying existing patterns like newtypes (opaque types), typeclass derivation and extension methods
* Improved type inference & lots of other quality of life improvements
* A macro system based on the idea of multi-stage programming. This has a lot of potential for improving both type-safety and performance. An example: beating existing database systems query optimization with ~500 lines of Scala code [1]
* TASTY, a new intermediate representation (AST) for artifacts. This means that Scala will have a much better version upgrade / binary compatibility story in the future. (e.g. TASTY is used for facilitating 2.13 <-> 3.0 bi-direction upgrade!)
* Significant compile time improvements over Scala2 alraedy[2] (and we're only at M1 release)!
Scala has already been a wonderful language to work with professionally with many great tooling (linting, automatic migration, 2 good OSS IDEs), and I think Scala 3 will certainly push the state-of-the-art forward in many departments in the coming years.
[1]:https://www.cs.purdue.edu/homes/rompf/papers/rompf-icfp15.pd...
[2]: https://twitter.com/not_xuwei_k/status/1323643312230772737