Let's put it this way. If you have been calling him Souji for over 2 years and suddenly... you are supposed to call him Yu. Everyone will have a different opinion on what they want to call him now. Some people will be too used to the name Souji, too lazy to call him anything else, or something else like that. Some people were waiting for an official name. Others like to use their own name or like joke names.
It is up to each and every person to do whatever they want, no ethics or disrespect involved... especially since if they know Persona, I think Souji/Soji and Yu should be universally recognized, regardless.