I'd rather he sold motes for coins. I don't know if it's true, but I sincerely believe the XP needed for more motes continues to increase with each one. Thus, coins are horridly easy to get compared to motes after a few weeks. Last week I spent ~50 coins at Xur simply replacing stuff I already had with pieces with slightly better dis/int/str rolls. Simply because I had plenty to spare. At the same time, I fell 3 motes short of buying the engram.