If you get proficient in a technology, you'll be employable regardless of the market size or niche. There's always demand for specialists. On the other hand if

If you get proficient in a technology, you'll be employable regardless of the market size or niche. There's always demand for specialists. On the other hand if you're more of a generalist, I'd say stay with popular technologies such as Python, JVM and .NET. You can't go wrong with any of these for the next 20 years. PHP has been making strides lately with JIT, Laravel and proposals for generics. So staying on it shouldn't prove a bad choice either. But if you're looking for greener pastures while maintaining great employability, my personal bet for the next decades is .NET/C#. And it tends to pay more than PHP on average.