@obrhoff The ActivityStream spec has a (very limited) Place object for very basic geo integration into the fediverse
https://www.w3.org/TR/activitystreams-vocabulary/#places
Unfortunately on the Mastodon side there seems to be resistance to implement anything geo related; various tickets, here are just some
https://github.com/mastodon/mastodon/issues/281
https://github.com/mastodon/mastodon/issues/29002
If you don't mind about participating networks like Mastodon not making use of it, there's nothing stopping you from sending geo data.