Using summaries for CWs is a creative hack, but that’s not summaries are intended for. The hack appears to work on Hubzilla but not Mastodon, but that’s hardly Mastodon’s fault.
Same for the NSFW tag. The real issue is that ActivityPub actually lacks and way to mark sensitive content (there’s some work in progress on that). Any hacks by various implementers to work around this fact are just that — hacks. And are not guaranteed to work on every implementation.
Compare that to Outlook allowing a sender to “withdraw” an email; if the receiver is not using Outlook, they will only laugh at that new message “recalling” the old one. Same problem: email (the protocol) has no “recalling” feature, and a dirty hack implemented by Microsoft doesn’t work with other systems.