Is that something you are willing to bet a major architectural decision on and/or your career?
I’ve been a Microsoft developer for over 20 years and a .Net developer for over 10. Even though I don’t see .Net “dying”, it’s also not a major growth opportunity.
Java is definitely not doing well compared to .Net even though it is open source - because of the mismanagement of Oracle. I see dart going down the same road.
As much as I prefer .Net to the JavaScript ecosystem, I am tying my horse to it. I’m focusing my attention on everything JavaScript over the next year (yes it makes me sad).
Until four months ago, I had never touched Python. But the more I got into AWS, the more I realized that the ecosystem around AWS and Python seemed to be the strongest. So Python it was.
Market wise, Java is still popular in the Enterprise and of course if you are developing for Android, you’re going to probably use Java (I’d rather use Kotlin), but for backend work the three most marketable languages seem to be JavaScript (Node), .Net, and Java.
Yeah PHP jobs are a dime a dozen but they don’t pay well. Python is a little better but it’s not “Enterprisey” enough for major corporations and the cool hipster companies where all the money is going are using Node.
I don't know where you're getting your information about Python from. It's popularity has skyrocketed in recent years. Search Indeed's API for title:python and location:London. 412 Python jobs compared with 278 for Node.js. What's also interesting is that there are currently 35% more Django jobs than Rails in London whilst at Angel.co they're about even.
Open source is not a panacea for a project that’s not popular and doesn’t have an active vibrant community around it.