Just adding this on the pile, I'd like to move away from XML towards something more like YAML or JSON. XML is just way too verbose for most things, in my opinion... source code edits, sure, but package-info.xml is ugly as hell.
Both JSON and YAML seem bad fits IMO for replacing the package format. Properly done, XML is actually really useful. Sadly, XML is rarely done right and usually turns into garbage.
YAML seems particularly bad as it relies on indentation to express hierarchy. If used for marking code edits, it could make for some messy code. For an info file alone, it might make more sense, but I just don't see it being as friendly to those starting.
JSON just doesn't seem to make sense as a replacement for the code edit stuff.
Either way, if you keep XML for the operations stuff, why would you force a different thing for the package info files?
Hopefully source code edits will be greatly reduced in the future, eliminated for most things in favor of events (hooks).
It'll be interesting to see how well the "hooks" hold up in the future as more and more stuff uses them. I forsee a ton of hooks being added to cover every possible scenario resulting in either huge code flow tracing issues and a lot of mess when developing.