...I like this discussion, skewed as it's been. I really believe that the developers of each new Zelda game relative to the main series of games ask themselves this while coming up with new ideas for game dynamics. It's a pretty necessary thing to ask, even though this "title" may never show up or be spoken in the games.
There are plenty of ways to go with this, naturally. The Hero of Souls concept is actually not a new idea; it's been an idea circulating around the fan-base for a while now. That is, the idea that Link can "DIE" and "REVIVE" himself frequently, traveling back and forth between life and the afterlife, able to use his soul to see the dead, pass through walls, possess people, etc. It takes cues from other games (SECOND SIGHT, off the top of my head), but it's still an interesting alternative. Nintendo handles death in the Zelda games rather coyly, so I don't think there's any real danger in making a game like this; it might even explain something about the multiple Links in the games, how their reincarnated spirits are passed down...
...anyway. My only contribution thus far would be that, at least for one game, the "Hero of...Whatever" title lean toward something that was a little more abstract, not necessarily having to do with the gaming mechanics. Something CEREBRAL. I mean, sure, the game itself could have a unique gaming mechanic/gimmick going for it, but what if Link took up a title that wasn't directly pertaining to what he could DO through that power/ability...but rather, what he ends up DOING on a deeper, emotional or symbolic level? I don't know how "deep" Nintendo is willing to go with the Zelda series (the most provocative one to me seemed to be
MM, since it was crammed full of death subtexts), but that's always an option. Make the gamer THINK about that name, APPRECIATE that name.
The same ol' route is fine too. Hero of the Beasts. Hero of Souls. Hero of...uh...Low Low Prices... Nintendo needs only to think on it.