Well, without chat bubbles, maybe you can just click on a message in chat window to highlight\target speaker? Or there can be generic nametags associated with people that you don't know ("Human 2", "Trader 17", "Adventurer 142").
After all, characters can be identified by some unique ID number, which is then searched in the client rolodex for a character's name, and the characters that are not currently in the rolodex will receive some generic nametags. Perhaps you can allow players to choose their nametag title from some list. Adoption of a new identity through the spy skills will give you a new temporary ID or, if you are trying to imitate someone, maybe you can even get their ID.
If, players are allowed to edit names in their rolodex, then, yes, you don't even need fixed names from character creation, except for some kind of /introduce command.