Please give materia a repair-like interface
One thing is certain, materia is costly. So too are the items in which we wish to place them.
The point of an MMO is to trust in your fellow player and to rely on their skills to aid you. But there are limits in how much we should have to trust in strangers. It may seem overly cautious, but if someone makes off with our expensive items we have no one to blame but ourselves.
This could potentially be a headache for GMs as there's no way to prove wrong doing outside of hearsay when the items were given via legitimate trade.
It's because of this that a materia interface needs to be a high priority. Something similar to repair where we put in the equipment, materia, catalyst and -- if desired -- a reward. This would remove any apprehension about finding strangers to handle melding.