One problem Mastodon may be able to solve that Twitter still hasn't is to make it easier to cross-link corrections for past tweets/toots.

See this birdsite thread for an example of the problem, where even though the author of a viral tweet would be open to posting a correction, they have no idea how to do so in a way that people will actually see (replies generally don't cut it -- too far below the fold).

https://twitter.com/ddale8/status/1348689248006893568 (or https://nitter.net/ddale8/status/1348689248006893568)