I'd like to start with a thanks here to Kntoran for his devoted GMing - I've only been playing for a couple of weeks but I've read back through years of thread. It takes a big commitment to keep this going. Well done - and respect to Icon and JB
too, though I'm not in their games.
Life can always get in the way, at least temporarily, but for dependable GMing I think Hunter's point must be right - they need to love the experience. But how can they know if they will until they try? I'm sure the experience of Play By Post is very different from tabletop GMing and some may not enjoy it as they expected. And if they find they're not enjoying the experience, what can they do?
I have a suggestion: when a (Non-established) GM posts a new Thread in the [+] Board, Card, & RPG Reviews detailing a proposed Role-playing Game, the GM and the players should agree to (Approximately) a 6 month commitment. If at the end the GM finds that (S)he enjoys the experience, then (S)he's welcome to continue. If however, the experience isn't what (S)he hoped, then (S)he can round up the game without disappointing the players or rebelling against the force.
I also think that Game Master's of on-going games should be allowed to announce a break from play - obvious whenever needed for life events, but programmed in advance to re-charge batteries. I imagine that GMing without a pause could lead to burnout, for some at least. This possibility may well exist already - its a very well thought-out site - but I haven't seen it yet.