Presumably the FT membership will "term limit" a Talkboard member that's problematic. That said, I pledge to stand for no more than 2 terms if elected, and will most likely limit it to one.
I think if Randy wanted term limits for moderators, he'd impose them. When (and if) he makes that an issue for the Talkboard, I'd consider it further. As a moderator, I think it's healthy to moderate different forums from time to time--some can be trying (I used to moderate OMNI, for instance, and burned out on it within a year or two).