It's really a good idea, and the extra text probably wouldn't really affect performance and memory very much if at all. The memory hog is the map, not the text.
I can think of only two objections from Paradox' perspective -
(1) The translation issues, as mentioned. But as has been said, that can be easily skirted by simply leaving a blank space for modders to work with.
(2) Support. This is a trickier issue. If they introduce a new feature, even an unimplemented feature as suggested, that means they have to support it, and deal with the inevitable "OMG I tried editing the text and now the game doesn't run WTF :angry::angry::angry:" posts. Not that I doubt the courage and hard work of the Paradox mods, but it's hard to support a feature that you don't really plan to use.
But all in all, it's a really nice idea. Some of the leaders are really obscure, and it's hard to find information on them at all. It would be great to be able to see who these people were.
Speaking of which, are there any plans for a public HoIWiki? That would be tremendous.