To me this is one Rabbit hole too far. Expansions make sense but getting into a world where we also ignore quotes is pretty ugly.
What do we do: hide the quote? hide the post that quoted it?
Next we would have to “ignore” replies to the ignored people and the list goes on.
Re MD5 idea … what if you ignored me … and somewhere on Discourse I said “I like bananas” is > I like bananas now banned from all the posts on the system and suppressed for you? This gets pretty crazy fast.