If your hiring decisions are always based on what people are currently familiar with, you'll always be stuck in the past. You may not even be able to use present day tooling and systems because they could be too new to hire people for.
You're much better off hiring people who are capable of learning, and then giving them the opportunities to learn and advance their knowledge and skills.
Everyone is capable of learning. I can hire someone who is capable of learning Japanese. They can then try to teach the rest of the team Japanese. Does that mean it's a good idea to switch all our internal docs to Japanese? Maybe if I was building a startup in Japan. Similarly, writing internal docs in English for a startup in Japan would be of equal difficulty and value. Hooray, we're learning! And struggling more than needed to build a product.
You're better off hiring experienced people who are highly productive. If they're highly productive with one stack, it makes no sense to change their stack so they're no longer productive, or hiring people who aren't familiar with it and waiting for them to become productive.
There's nothing wrong with using old, well established things. They're quite often better than new things. As long as they're still supported, just use whatever builds a working product. It's the end product that matters.
> Everyone is capable of learning. I can hire someone who is capable of learning Japanese. They can then try to teach the rest of the team Japanese. Does that mean it's a good idea to switch all our internal docs to Japanese?
The difference between Japanese and English is much, much bigger than the difference between one Unix OS and one Unix-like OS. This is a remarkably disingenuous argument. If you really don't understand the difference in scope, there's no point in discussing anything with you because you've managed to disprove your opening sentence with yourself as the counterexample.
You're welcome to see it that way if you want. But if you think you can get to know a completely new kernel, OS, etc in a short amount of time, backwards and forwards, you're equally as disingenuous. You can get by editing a few lines in a pinch, but you could equally just learn a few Japanese phrases. Proper understanding requires a deep knowledge that comes from practice and experience with subtle complexity and context.
(Japanese isn't so radically different from English, it mostly just has more words for more contexts. In many ways it's simpler than English. It would be harder to go from Java to Haskell, with their many different language paradigms)
You're much better off hiring people who are capable of learning, and then giving them the opportunities to learn and advance their knowledge and skills.