One of my big drivers away from XML is that processing used to be insanely expensive. Over the years this has improved some, but XML parsing is still significantly less performant than any other option, especially compared to JSON or YML. Used to be a few orders of magnitude more expensive on compute to read, and that's why many folks in the industry were happy to move on, esp for cases like message passing. I've pulled XML out of a few apps over the years in apps with a lot of message passing and the throughput and performance improvements were measurable and significant. For that use case Protobufs are much better than XML and have a schema though it's a binary format, so not usable for conf files.
Yes, that's very true. I actually have used json representation at previous gigs, I just wasn't up to adding the extra qualifiers. Whenever I've needed to use Protobufs, I've always found them very nice work, really. I certainly have a much warmer opinion of them than XML.
