for simplicity sake for the SE team, which might also encourage them to go through with merging obis/gorgets, this would happen with only combinations of Rare/Ex items since they cannot be stored/trashed(unless you want to work for them again).

The effort we spend in farming all those organs should count as enough investment. incorporating the idea of exp trials (what conditions will xp need to be gained to count?) would serve as more work and act to deter people from making a merged obi/gorget. furthermore, i hate doing exp trials for dyna equip. synthesis recipes would work best as ToM trials can only upgrade one item a time and not combine more than one (unless you turn it into the box).

i'm all for an "all or nothing" approach to merging. one elemental obi, one elemental gorget. (maybe those m.acc grips too) If I had to work for SE, designing separate trials or multiple syntheses to combine just two or four obis at a time and making those respective products might end up being more a pain in the butt than not.

if SE wants to put in the work to combining two items at a time, they could very well make skillchain named obis. this would only add 4+2+1 items to the game (and reduce inventory for those who only spend time getting those certain obis) remember that my goal would be to reward those who got all the obis/gorgets.