It would be interesting to see materia slots (but no possibility of overmelds) on new endgame equipment that cannot utilize existing materia types. It would be interesting to see gear diversity by means other than the few stats we have currently on equipment. Adding options such as: DEF, MDEF, Slashing/Blunt/Piercing resist, evasion, food duration+, Conserve/Save TP, Conserve/Save MP, Occasionally annulls magic/physical damage taken. These materia could come from spiritbonding and converting old raid gear (Binding Coil, Second Coil, Labyrinth of the Ancients, Syrcus Tower, etc) which would also keep people doing them.
For example:
Lv60, Item Level 150 body
DEF+ MDEF+
stat+ VIT+
substat+ substat+
O Magic Defense V materia (+5)
O Magic Defense V materia (+5)
Lv60, Item Level 150 feet
DEF+ MDEF+
stat+ VIT+
substat+ substat+
O Conserve TP IV materia (+4% chance to use half TP on a weaponskill)
O Food Duration III materia (+90 seconds)
