When I need to /tell someone in front of me I just do "/t <t> blabla" so it's not really a problem. For people I don't see and need to party with, generally they talked at least once or shouted or what not but for me to have awareness of their existence I had to see their names on my log before. So I grab my mouse and copy/paste the name.

For people I often chat with via /tell, it would be nice to be able to add nicknames.

Exemple: My character is Seyra Mihgo, a friend could add my nickname, say "Sey", in a specific menu (other than Friend List menu) that writes it in a database on your Final Fantasy XIV user folder. When he wants to /tell me he would just type "/t Sey blabla".