These all sound like fine DRAGON articles.
I'd like the core to set the baseline game, and a few common sense ideas on how to change things (the 3e DMG does this really well). I really don't want to see half-fiendish ochre jelly PCs again, so if we put weird stuff in supplements and focus on the baseline or common options in core, we can strike the right balance.
We'll have to accept some things come later.
This portion was stated several times in the 3e DMG and, apparently, many people either ignored it or skipped over it. I also don't think it is enough for it to be just in the DMG. It needs to be stated in the PHB as well so that the players are made aware.
I think more than stating 'The GM can do what he wants' the DMG needs to be offering practical information on world building. That sort of advice has been very much missing from the last two editions.