It's not a matter of "before Mastodon" and "after Mastodon", at all.
I was trying not to state this so bluntly, but basically, platforms that came before Mastodon had blockquotes before Mastodon existed. We did not get rid of them in 2016, and we aren't getting rid of them now.
So, even if you implement this proposed feature, which is your right, some platforms will stay with the tried and true blockquotes.
It's not just that they may not care. They may not know what they're being asked or know what the consequences are for choosing either option. Then they sit there for 30 minutes searching the internet for what the question means.