AMP is embracing and extending website hosting.
Google News is embracing and extending free web news outlets.
Chrome is embracing and extending the open-source web browser community.
Android is embracing and extending the open-source mobile OS development community.
I understand what you mean by "the intent is important", and certainly no senior Google executive is sending emails with directives as explicit as Bill Gates did.. But they don't have to, because the EEE playbook is now well-understood by the rank-and-file. When Gmail PMs gradually introduce more and more proprietary features into the product, gradually widening the gap in functionality with IMAP clients, they know what they are doing. It's not an all-out assault on open email above all else. But the end result is the same.
Bottom line, EEE in 2018 looks different than EEE in 2000, but it's there, and it's just as dangerous. We should not give Google a pass just because they're more subtle in their implementation.
Gmail is very far away from extinguishing open email, because that's such a huge target, but it certainly managed to make a dent. How many users have forever left the open ecosystem of smtp/imap/pop tools and service providers because of Gmail's growth? If Gmail hypothetically reached the market share necessary to mortally wound that open ecosystem, do we have any doubt that it would eventually do it?
And remember, email is the largest open ecosystem in my list. Where is the fully open alternative to iOS? Answer: it doesn't exist because Android captured all the momentum from the emerging community, and channeled it into a platform that is now closed for all practical purposes. In this case, extinction has already happened.