Actually, I'm mainly using Scala now with the Java 8 JVM. Regardless though, the reason for either Java 8 or Scala for my current project would be because of what I was building. I am a polyglot and will in most cases assess the languages, tools, libraries, etc. that will get the job done well and fast. In my particular case, I primarily build backend/platform applications. Java/Scala, and more importantly, the tools and libraries that come along with them (especially since for the most part, they are interchangeable, but more so Java-to-Scala), have proven to help me get stuff like high throughput REST APIs, large scale data processing tasks (i.e. batch, scheduled), and pretty much non-front facing web applications running. That's probably the gist of what I'm doing at my current startup. I haven't yet used Java in the frontend (e.g. Play, JSF, etc.) and understand that they work, but prefer server scripting, and more recently, Javascript, for that kind of stuff.
What it comes down to is: you just got to find what works for you and the thing you're trying to do. Honestly, never ask just one developer how he or she would do something. Ask a varying bunch with different backgrounds. If they happen to intersect in opinions, that might be a good place to start. As for finding developers; I haven't had to do that because I work within a small group (I also have a day job doing Java, but it isn't a startup). But I'll tell you this, there has got to be a demand for JVM developers, because recruiters, including those from startups, seem to like doing LinkedIn queries for JVM-related buzzwords. I can't tell you if it's working for them though, but it at least shows other startups are using Java and the JVM.
I realise I'm not answering this question directly (although I am using Scala and Java 8 in my own startup project), I thought it might be applicable to leave these here:
Ah, yes, didn't consider that. But what about 'this'?; for what reason could the JVM choose to GC an object that the calling thread is currently running in? The example method exists in an instance of 'this' and isn't static.
I only have an amateur interest in JVM development, but doesn't this bug break some rules around GC 'object roots'? Even if 'child' and 'something' are referentially copied to local variables on the calling stack, I believe 'this' should continue to act as a root for both of them. I think.