Syntactically and semantically Scala is one of the best language's I have ever worked with (although I spend little time with it).It's middle approach to OOP and FP is best approach for enterprise projects.It does not try to shove FP in your throat, but provide best platform to do FP when it is much more efficient than simple OOP.
However when it comes to JVM (especially in Linux desktop). My answer is big fat NO.
Of course, I am talking about desktop experience.JVM in server side is great and robust, I don't have anything against it, other than praise.
Were it not for the Java-land compatibility & ecosystem requirement (and all the baggage associated with it, such as not alienating Java OOP programmers), I wouldn't use Scala. I'd probably ditch the OOP part of the FP+OOP hybrid that causes problems in Scala, and use something like Haskell instead.
I honestly have no interest in a native/JVM-less Scala. There are better languages for that out there.
I'd be willing to learn how to write GUIs in any language.
PS: I see that Leksah (http://leksah.org/), a Haskell IDE, is written in Haskell using GTK. The screenshots look decent enough. Not sure if it's unpleasant to write a GUI app like that in Haskell.
*Assuming my agreement lowers the probability of being ridiculous, which is an open question… ;)
Disclaimer: I work with Scala in my day job, and I like it -- it sure is nicer than Java -- but I don't know if I would use it in situations where the JVM wasn't mandated or needed.
Aside: Shenendoah was supposed to be an improvement over existing GCs in pause times, but it's not yet ready if it's alive and it's for very big heaps and when you want low latency over performance/throughput.