As I understand it, the “helpers” of the GB would fall under the “Nethinim” class, sometimes also referred to as the “given ones.” Here is a quote from the 2006 WT, Feb. 15, p. 28, par. 11, under “Walking in the Path of Increasing Light”:
“The year 1992 saw still another refinement, one that is comparable to what happened after the Israelites and others returned from exile in Babylon. Back at that time, there were not a sufficient number of Levites to care for temple service. So non-Israelite Nethinim were given more to do in helping the Levites. Accordingly, to assist the faithful and discreet slave class in caring for its increasing earthly interests, in 1992 some of the "other sheep" received added service responsibilities. They were appointed as helpers to the Governing Body committees.—John 10:16.”
So, with the number of anointed ones not really dwindling anytime soon, it looks like the GB will always have enough “spiritually mature” ones ready and willing to help them – either of the anointed class, or second-best: the good old Nethinim class.