It's a fine point, and quite reasonable. It is however I think important that we don't all take your approach.
How likely is it that Fossil will displace Git? If you believe it is likely, then learning it, and using it for projects, may be time well spent. But even then, it'll take so long that you will still have plenty of time to adapt. So perhaps it is something you should keep an eye on, but not worth investing in now. If you find Git to be a pain, then a better investment right now, which pays off right now, would be to figure out what you can do to get along with Git, and thus most developers.
You have to treat learning as an investment. Which means, you have to think about about returns on investment. And just like regular investments, it doesn't matter what people who don't pay attention think.
But sysadmin'ing Windows vs. Linux is basically two different jobs. You certainly wouldn't hire someone to be a Linux admin who'd only worked on Windows servers before.
Also, I wouldn’t put the choice of SCM at the same level as the choice for OS.