1) I do not think the programming is going to be a straight copy-pasta for the differences of melding a single piece of gear at percentage chances vs. repairing a gear with varying degrees of percentages and various potential grades of materia. No, the system does not, currently, in FFXIV exist, and to say "It'd be easy" without any way to substantiate it is completely personal opinion. Accept that it would take more work, however, than something that IS Available in the game.
2-3) Again, the model of the idea is following behind the model of Materia Melding. If Square puts in a Request system for Repair, it is likely to have a system that enables someone to include a 'tip' for the work. It is an exchange between players, is what oyu need to understand. This means that it could be used in a way to move gil. Why do you not understand this?