Despite what some fanatics may claim, operating systems other than Windows are still second class citizens (saying this after five years of doing .NET development almost exclusively on Linux), especially for dev, and operating systems other than the big three are not supported at all. So no BSDs (even FreeBSD) or Solaris if you ever need it.

Since the open .NET is pretty young, and they still have trouble with community perception due to their past actions, finding high quality FOSS libraries may pose a problem depending on what you're doing. Pretty much everything from MS is open and high quality, but they don't provide everything under the sun.

And with Java you always have alternative runtimes in case this Oracle deal goes sideways for any reason.

So you're all good, don't worry about it.