Well, first off, we can already customize lordship titles, to a certain extent. We've got a dropdown menu that allows a few choices, such as the republican one where they are all senators.
I think having a few more presets could be the best option, though. The problem isn't only that you don't know what the titles of your *peers* is, which can indeed be somewhat fixed with a bulletin note, but that one does not only interact with nobles of their realms. If each realm has their own weird titles, it stacks up, and any benefit you gain from having the power to use special titles for yourselves is kinda lost by having to learn a dozen new titles for everyone else.
Honestly, I'm not too sure that we need more lordship titles, though given that they are now largely interchangeable (count vs baron vs earl, for example), perhaps we could simply allow more customization with those, plus maybe a few more non-european prests. So that a realm could decide mountains are held by earls and townslands by counts, for example.
The main boon, however, would be customizable ducal titles. I think these are the ones realms have the greatest tendency to want to make their own names for. Same realms have called their dukes kings, for example, others governors. Viceroys could also work, and governor general as well. Adding realms the ability to customly name their duke titles could be made non (or less) confusing by modifying the way it displays in signature, with: Bob McGee, King of the duchy of Boogeria. "of the duchy of", in the signature, would tell readers that the preceding title is a ducal one, no matter how misleading the chosen title is. Alternatively, again, we could just brainstorm a dozen ducal titles and offer a preset. Or offer a dev-review feature, like realms that want to upload new flags.
