I assume he is speaking of the base system. Though I wonder how good an idea it is in practice. E.g. I cannot really imagine configuring, say mutt, via JSON, XM

I assume he is speaking of the base system. Though I wonder how good an idea it is in practice. E.g. I cannot really imagine configuring, say mutt, via JSON, XML, or whatever. The power of such configuration files is that they are often domain-specific and allowing a custom format makes them compact. Of course, for automation or writing user-friendly interfaces, a unified format is better.