Since the browser maker will no longer control the blacklist, they will now have users telling them that sites are broken (because they've been blacklisted), and they won't be able to do anything about it on the blacklist side. So, what they will be incentivized to do, is to make whitelisting a blacklisted site (especially those that only get loaded through invisible iframes etc.) have a much simpler/easier/clearer UX, so that their complaints go down. This is good for everyone, but it's not something they'll do when they still have the option "just remove X from the blacklist."
It might be a bad assumption that users will demand a more liberal blacklist. That's certainly not how e-mail blacklists have worked out. Sometimes the people most in favor of the blacklists that hit all sorts of innocent mail senders are the users sick and tired of spam.