The mark cap itself prevents any meaningful gain to glimmer or rep. I don't see any way this could be an exploit with the pathetic conversion rates and caps already in place. If someone wants to blow 1000 mats on marks, then turn around and blow them on mats just for rep, so be it. After that, they're done. No more marks for the week and their stack of 1000 just turned into 200. Still have to go farm 800 for next week.