Diff between two roster windows

For enabling dynamic address book we need to provide a diff between two roster windows.

It shouldn't blindly apply difference between current and new, but rather get a superset of all rosters which are in possible window of interest for the consensus (most probably every roster which is not related to ancient rounds and then everything in future).
Then, do a diff between such supersets, as the windows are changing. This means that peer will be added well in advance of when it is needed and removed well after it is not needed anymore. Network layer cannot decide such things (as it is not aware of the round boundaries, consensus etc).

In theory it is as simple as creating a superset of all peers from one windows, superset of all peers from new windows and doing a diff between them, but we need to solve the case of metadata for a single peer changing between the windows (for example, TLS cert change). Not clear how to solve that.