Well, good news about that, a simplified version of adblocking through content filtering[0] is already part of Ladybird (and has been part of Browser[1], the version of Ladybird integrated in Serenity, for a while). There is even a video[2] where Andreas implemented it!
[0] https://github.com/SerenityOS/serenity/blob/master/Ladybird/...
[1] https://github.com/SerenityOS/serenity/blob/master/Userland/...