Turning Scala into a duck-typed language will obviously fail. It would be analogous to turning Python into strongly typed language that rejects programs with type errors. Scala compiler depends a lot on types, for example all implicits are type driven. Scala without types would be a very different language.
Scala scripting is not about fundamentally changing the language, but rather removing the need for structuring source code within a file, and files within a project. You can do scripting in strongly typed languages like Java (JShell), C# (PowerShell), Scala (non-standardized yet?) and so on.
Performance and memory usage have lower priority than developer friendliness and productivity when it comes to scripting. Python has low performance and high memory usage, but it’s (the most?) popular language for beginners simply because you can finish the task sooner.
In general Scala is a bad language for scripting because of high compilation overhead, so insisting on using Scala scripting in e.g. production wouldn’t be sensible. Instead Scala scripting should be oriented towards beginners (who only start to explore Scala), to make Scala more popular. Scala doesn’t need to be a language for everything.