I learned recently that one of the killer apps for Scala seems to be in hardware design. Chisel [0] is the core technology of the best open source RISC-V chips. Chipyard [1] is designing leading edge type OOE and AI chips and all of the code is written in Scala. Personally, I can't wait for some of these designs to start being mass produced and put in laptops and phones.
[0] https://en.wikipedia.org/wiki/Chisel_(programming_language)
[1] https://github.com/ucb-bar/chipyard