Well...if Materia attachment rate is based on wearing Optimal Rank gear then this could be a useful side benefit of ranking second/third/fourth classes. While ranking them, you are turning that mid-grade gear into Materia and removing the gear from the game. Could be a good incentive to wear OR gear during the middle ranks and spur the demand for those items. And if you're planning on turning r50 gear into Materia than I wouldn't say that you're doing it with gimped gear...just less than optimal gear since you'd be using trying to increase attachment to a NQ r50 item so that you could then attach it to your HQ r50 item. (This all assumes this system is designed well and doesn't reward attaching lower rank gear more than higher rank gear.)