It’s a neat idea but I’d worry if it scales at all to anything beyond a hundred or so followers. At that point it’s offloading the spam filter onto the author, which will end up not publishing any replies at all simply due to the effort necessary.
The ability of the OP to accept or ignore replies is in addition to, not instead of, regular spam filtering techniques. Certainly we'll want to automatically block bots and other bad actors that violate our policies to reduce the burden on users.
