If this means users gets more power over what CAs to trust then that is a good thing.
And depending on how that law will be interpreted by courts, manually distrusting might be considered illegal.
It is just a display change, all the law says is:
"For those purposes web-browsers shall ensure that the identity data provided using any of the methods is displayed in a user friendly manner."
I don't see how adding a warning icon or block icon instead of the lock hurts would be banned. To me it seems like so much here is based on baseless assumptions.
I would also urge you to refrain from using terminology such as "baseless assumptions" when your own assumptions are so easily refuted by directly reading the text of the proposal.
Do you really think your average user is going to go into the browser and manually distrust root CAs? We have learned again and again that good security is "secure by default", not "secure after arcane configuration".