I do know Yoshi has a big noticeboad of player-made fanart and fan letters friom around the world mounted on a wall in his office (as it was shown during an interview as I recall) that he uses to remind himself of just how much this game has touched so many players and to keep his esteem and morale up when problems are plaguing him.

I think the best bet is to address it directly to Square Enix in Japan, their contact details should be on their website, and they'd be able to forward it onward to the FFXIV team.