Hi there,
if it's not yet possible, I think it'd be good if you could link characters so their attendance shown is combined (if someone plays multiple characters in the same raid group) - for example by being able to edit a name to "character-server, character2-server2" or similar.

If it already is possible, please tell me how! ;)

It sounds like the main-alt related functionality.
Check Config -> Edit (Roster).