Well, I think the superhero RP is pretty much evergreen (it provides an almost endlessly adaptable sort-of-contemporary setting in which to play out archetypes and fantasies), but there'd be nothing wrong with a Gundam one. I see that a Gundam big game was attempted here before. A logical first step for someone to take might be to have a look at that one and see if there are any lessons to be learned from it for a forum setting.
(Not that "someone" will be me. I'd consider running something based on Mekton Zeta at some time in the future, maybe, but for right now Pacific Rim has taken care of my mecha fix just fine...)