In abstract, I guess maybe there would be some benefit, but I've been using Linux for decades, and it really hasn't been an issue for me. I've definitely had times where configuring stuff is confusing, but it's not a function of the basic input format not being JSON or XML or TOML or YAML or whatever. I think that the only time that I recall tabs being obnoxious was not with config files, but with Makefiles (they do, in fact, require tabs).
The majority of software is packaged with an "example" config file, often with comments in place. Traditionally, software will also ship with a section 5 man page for its config files. So, for example:
$ man 5 fstab
Will describe the format for /etc/fstab.
EDIT: I think that the biggest hassle I recall was in configuring a sendmail mail server, quite some years back. The issue there wasn't the basic format, but the fact that due to organic growth, even basic configurations were enormous (just to get the sort of common configuration that most users wanted) and required quite a bit of reading through the option documentation. It was common to use a frontend to generate the config files, and a number of subsequent mail servers aimed at having their default, no-configuration-options state being closer to what people wanted, dramatically reducing the number of options that had to be specified.