While true, there are quite a few programmers who can. I'd go for a core library + PSR, so that the average developer can still use the core library. That way a

While true, there are quite a few programmers who can. I'd go for a core library + PSR, so that the average developer can still use the core library. That way advanced developers can use something PSR compatible, and libraries that depend on the core library can still function.