That's great, thank you! We've had various people ask about us getting on Mastodon but frankly I really dislike social media and have only the vaguest understanding of how Mastodon works.
If we did, then someone would have to volunteer to run the account, and also the account must be able to delegate posting powers to another user without exposing the account's master password (like Tweetdeck or Facebook are able to do). If that's possible and you're interested in helping, please send me an email!
For what it's worth, they have an Atom feed - https://standardebooks.org/feeds/atom/new-releases
Thank you for your beautiful project.
For a few years, every January 1st, for public domain day, I have been promoting SE on social media, the thread on Mastodon is the one with the most involvement. https://fosstodon.org/@paulox/111680544393923401
It would be nice to have an SE account on Mastodon that posts about every new book published, since IMHO it's the social network more aligned with the spirit of SE.