I, for one, am displeased with .yaml. I recently had a major footgun incident where a Debian VPS was rendered completely unbootable because of Ubuntu netplan's highly-annoying use of YAML (where I had done the slightest misconfiguration, and to my eye it looked perfect,
and my changes successfully passed the parser of "netplan try"). Yes, that's right - the server needed to be rebooted in rescue mode; it wasn't just merely stranded with no working network interfaces, where the web-based serial console would have been enough to undo the footgun gunshot. Nightmare!
The solution was to uninstall netplan.io Debian package where it didn't belong - get that YAML out of there. My hosting provider, OVH, figured it would be a good idea to shoehorn netplan - with its accursed YAML - into Debian for Network configuration. Bad move.
+1 for TOML. I love it's usage in innernet config files to set up new clients with a single generated "invitation" file.