I suggest tooling as a theme. Super rewarding and fun to work on tools that help programmers master and be productive with Scala (REPL modernisation, Scaladoc using tasty?, help with VS Code IDE support via LSP, help with scalafix: refactoring & linting, configurable error reporting / suppress warnings, nicer error messages,…)
Some ideas for REPL modernisation:
- upgrade to jline 3 for multi-line editing and history, highlighting as you type,…
- make it more like a worksheet with e.g. watched variables that update as you change your program
- make REPL embeddable in your own code to poke around in a running program
- (advanced, happy to help with this) make the compiler more supportive of REPL-style line-by-line coding, instead of encoding it with deep nesting of interpreter wrapper objects (https://github.com/scala/scala/pull/5220)