I personally am annoyed with these third installments. Yellow and BW2, maybe platinum are the only exceptions. I mean, crystal and emerald both suffered identity problems and as such the story and main legendaries were all out of whack.
I think they should just do it right the first time and not need to say afterward "aw, damn, wish we thought of that BEFORE we released the game" and add in arbitrary features to a game you already own. However, it appears to be a somewhat successful money grab from GF.
If this is pertaining to letters, then I think a better idea for a 3rd game or sequel could be on wii u. Sales boost, plus a GOOD reason to buy it, IMO. So many possibilities for that. Pokemon U or W maybe,