There are two separate things here. First the real ‘sync’ that was part of the early 2.0 version. You pressed a button and ideally only things that had changed would get updated.
Problem is, it never worked properly because in some cases the modification time info was not even available. rekordbox for example, doesn’t even store this info anywhere so there is no way to know what has changed when. Just looking for changes is not enough, you need to know when this happened so that the syncing is correct. So basically this was never really doable in the end. I tried.
In a 2.0.24 and after, I replaced the sync with an import/export method that would work better but be an all or nothing. You had to import or export the whole collection. That wasn’t ideal either.
Fast forward to 2.1 and yes, both sync and import/export are replaced by drag and drop but this is a great building block for future improvement. Basically if you guys can pick and choose what to copy from one collection to another (and without the need to go through the Rekord Buddy collection if you don’t need to, which makes the process much faster) then we can imagine a feature that will show you what has changed, when it can, and allow you to only update all or some of those changes yourself.
So that’s the plan moving forward.