Maybe, it was a bit off the cuff, and I'd need to think more about it and look at some actually employment and pay data to have a better sense of the validity of the claim. However, I think in general looking for a exploitable niche is a solid plan.
I'd support the notion entirely though. There are so many Enterprise Java jobs that have the 5 years of experience qualifier that it's a significant impediment for a self-taught.
I ended up seeing both sides of this - I taught myself PHP and MySQL for a project I worked on for 3 years of college in my spare time...while I was learning Java and going through the CS program.
When I came out, oddly enough I ended up getting a PHP job despite spending a lot of time "wanting" a Java job. Definitely got to experience both sides of that coin.