After reading Yoshida's message on this thread, some ideas popped into my mind which might as well be interesting.

Yoshida stated that scaling damage with VIT would cause HP inflation if I interpret the message correctly. There are also people using iLv 270 STR accessories to get more damage, but that causes problems for healers because they tanks will have reduced HP which Square Enix doesn't want. Then why not adding a 4th stat on the accessories providing a bit of STR as well? That way, Square Enix could let higher iLv accessories scale damage (STR) while not inflating HP (VIT stays the same). Put a limit to STR, so people won't all start melding STR Materia VI on all their accessories, but do leave some room for melding these materia.