As an ATCO, I would welcome ATSA licensing, if only from the point of view of reassurance that the colleague sitting next to me went through a similar examination to me in the past year.
I may be being naive here, but would it not also encourage in some a bit more pride and professionalism? Ok, maybe that's not how I meant to say it, as many of our ATSAs take the utmost pride in their work as it stands..... I guess I'm trying to say that it would be an official recognition from the company, and us as controllers, that that professionalism and pride is valued.
After all we are on the same team, and, certainly at my unit, the input from ATSAs can have serious ramifications if a mistake is made.