I suppose it depends on whether you're thinking of an adversarial situation, or assuming sites that don't actively try to defeat the user's preferences.

Most news sites don't try to defeat my adblocker, to offer one example. It would certainly be in their interests to do so, but it's rare that they actively try. When they do, they usually try to block access while asking me to turn it off, rather than trying to sneak ads past it.

I'd probably stop visiting a site that actively tried to force video to play when I've asked my browser not to.

> Muted autoplay is unblockable because I can write a script that flips through frames.

Since I don't allow scripts to execute in my browser by default, I've already blocked your autoplay workaraound.

Muted autoplay is unblockable because it's equivalent to using an image that specifies `Content-Type: multipart/x-mixed-replace` and constantly streams new image frames to the client.

Fine as long you'll be able to cover extra bandwidth cost - and it would be easier to distinguish this from valid parts of page and block it.

GIFs are blockable with image.animation_mode in about:config

I wouldn't say unblockable.

Sure, all you have to do is either block by default Javascript or all images. Obviously those features belong in a browser extension, not the core feature set of a mainstream browser.

Counterproductive.