I think we have been fairly lucky with reply spam, tho some would likely disagree (if they have been a target of this). Eg. The airdrop bots and others may choose to target specific pubkeys.. Imagine someone wants to attack your inbox, it's trivial for them to reply spam and DM spam you using blaster or any public relay. Even with relays attempting basic rate limiting, I think this is a scenario that will happen (if not happening already). Those that have been targeted, I do see them being driven insane by it..