Scenario: two ore more players are on a server and share an atlas.

I propose an option where those players can see each other in real-time as a marker on their atlases. Each player could only see other players when those hold their atlas in the hotbar.

There's a related suggestion on Discord

Rather then combining with friends book you can make notes of it but it takes time. Basically you have both books in both hands. Primary book has the main map you want to copy to your friends book that is in the second hand. Right click to copy this will take a certain amount of time to do. while holding both books you can hold shift and right click to only give a location pin to a friend. This will point out where the village is on the friends map while not copying your full map with your secret base on it.

I like the idea of sharing piece of data between atlases. maybe that could include some player position.

You can already do that, just not in real-time:

1. Share the same atlas with your friends (atlas cloning recipe)
2. Shift-click on the new marker button and it will create a marker on your position
3. ...
4. Profit

Tbh. I don't see that real-time position sharing fit into the theme of this mod.

I certainly agree not everyone wants this, so a configuration option (possibly disabled by default) should be present in any case. Another option might be a range, at which you can see other players on that atlas. I do think it would be a nice addition for some servers however, as manually creating a Marker every time you want to sync up with a coop-partner is quite cumbersome.

I haven't looked into it, but i'd also be fine with implementing this myself, possibly as an Add-On (but i doubt the current API has enough flexibility). I'd still prefer it to be included though, as i don't have the time and energy to properly maintain a mod right now.