Though I imagine that only works so far as you feel you can trust the Foundation to stick to those principles, so that's complicated. :D
There's also a bunch of FAQs here that sort of get at how the funding streams are supposed to integrate into the existing structures and how it's supposed to avoid pushing out the free services: https://meta.wikimedia.org/wiki/Wikimedia_Enterprise/FAQ
(As I said elsewhere, I work for the WMF but I don't work on anything related to this so I'm just commenting as someone who has more experience searching through our public info than most HN commenters would...)