I'd like to third the proposal of a record of a nation's past nation and ruler names being checkable. Maybe even make it so it can show up in nation/ruler name searches. Since ID number can't be changed you can't clear yourself with this anyway (and I'm pretty sure letting people do that wasn't the intent of the change- I get the impression it was intended to let people who actually didn't like their ruler or nation names to change them.
This could be useful even for friendly purposes; alliances who keep lists of members or specific groups of members (trade circles or the like) by nation/ruler name and don't save ID numbers, or people looking for old friends' nations (or current friend's nations, even) and not being able to find them. Come to think of it- if you didn't know someone outside of game and didn't have their nation ID saved anywhere, that could actually be a problem if someone changed both ruler and nation name and then realized they had no way of verifying who they were. Seems unlikely to be too important though (unless there are alliances that don't have any forums at all or something), but worth keeping a record regardless.