The primary concern here is members who have showed that they are a valuable asset to the forum and are both good posters and good at rewarding others for good posts are not being appointed merit sources or are being appointed long after they have made an application.
I don't think you can chalk this up simply to theymos being too busy. Some sources were appointed within a day of application. I think he is simply happy with the amount of sMerit currently being generated.
My worry with your system is that you would end appointing people who didn't want to be sources. Many users would simply nominate their friends, some would nominate trading partners, and many more wouldn't understand the difference between customized merit lists and customized trust lists, and just put the same people on both. You would end up giving sMerits to people who have little interest in spending them, and total merit circulation would drop.