Pros and cons for different configuration formats?
Note, this is pure opinion and speculation on my part but I suspect that the single biggest reason for the plethora of formats is likely due to the lack of a readily available, omnipresent configuration file parsing library. Lacking that, most programs have to write their own parsers so it would often come down to balance between how complex the configuration structure needs to be (hierarchical vs flat, purely data vs embedded logic like if statements, etc), how much effort the developers were willing to spend on writing a configuration file parser, and how much of a pain it should be for the end user. However, probably every reason you've listed and could think has likely been the motivation for a project or two in choosing their format.
For my own projects I tend to use .ini simply because there's an excellent parser already built in to Python and it's been "good enough" for most of my use cases. In the couple of cases it's been insufficient, I've used an XML based configuration file due, again, to the relative simplicity of implementation.
I've seen people using *.cfg (Python Buildout), *.xml (Gnome), *.json (Chrome extension), *.yaml (Google App Engine), *.ini and even *.py for app configuration files (like Django).
My question is: why there are so many different configuration file formats? I can see an advantage from a xml vs json approach (much less verbose) or a Python one (sometimes you have a Python app and don't want to use a specific module just to parse a config file), but what about the other approaches?
I know there are even more formats than those configuration files I exemplified. What are really their advantages in comparison to each other? Historical reasons? Compatibility with different systems?
If you would start an application to read some kind of configuration files (with a plugin ecosystem), which one would you use?
Which ones that I gave as example are the oldest ones? Do you know it's history?