Ask HN: How do career prospects look in non-enterprise/startup development?

So I'm your another typical enterprise dev, making good money in a safe and undemanding job, but at the same time being bored to tears... I've been pondering switching fields for a long time now. I'd be interested in something where I'm tasked in writing the actual software and not just gluing together frameworks and libraries. I'm affraid that this requirement pretty much rules out most typical enterpise and startup jobs... Ideally I'd be streching my brain, writing libraries/engines/frameworks or some other "core" software. I'm also fond of math and have some background in machine learning (did Msc in it), so it would be nice to utilize it, however if I end up working in a non-mathy field that's fine too. My main languages are Java and Scala, and I have (partial) working knowledge of C, C++, OpenGL and a bunch of other fields. As for learning new skills, I have plenty of savings so taking an extended time off to study a new field and/or doing a PhD is definitely on the table.

What are my options at this point? I'd especially like to hear from people who are insiders in some of the more "hardcore" fields. Also, I'm interested in pragmatic assesment of difficulty of getting into a given field, and job/salary prospects (I'm based in EU, wouldn't mind moving to US if there are H1-B possibilities in a given field) - i.e. I know that working on for example Linux kernel would be a very cool job, but as far as I know it's an extremely small niche populated with people with 10+ years of experience. I believe the same might be true for computer vision (another field I consider very cool), not to mention that the salaries listed in the UK for them are less than half of what I make in enterprise software.

One last thing - I know that there are quite a few people like me in the enterprise world. Hopefully a lot of people will benefit from this thread.