There are quite a few Java libraries and I am building my Scala code on BitcoinJ, but obviously, native Scala libraries would be quite a bit more elegant. Has anyone tried?
As far as I know there are no Scala Bitcoin libraries currently under development.
As @ripper234 suggests, you could make do with the (canonical) BitCoinJ library which is currently under heavy development. This approach is often the case with JVM languages, whose primary purpose is to leverage the quality of the underlying support libraries rather than reinventing the wheel.
However, given that Scala now has a .Net implementation, then this argument becomes weaker. Therefore I would take the stance that there is room for a native Scala implementation, just as there is one for C# (BitCoinSharp).
Although slightly off-topic this forum discussion of a C reference library (not C++/C#) brings up some interesting ideas - does it skim over a Scala library in passing.
This an old question, but there is an implementation now:
You could also check out my project: https://github.com/colinrgodsey/scalaminer
Looking to expand functionality too