I’m of the firm belief that one factor in the declining playerbase on GGPO (at least for ST) is that more and more people are moving to Windows 7/8, and the horrible frameskip that is inherent in GGPOFBA feels even worse on Win7/8. On top of that, if they’re running it on a laptop it will be on top of the laptop screen’s display lag, making the whole experience a laggy and stuttering mess compared to arcade.
I’m using XP with a lagless monitor, and GGPOFBA still suffers badly from input lag compared to ShmupMAME, along with the usual frameskip/stutter. I think it would definitely help if Ponder ported the code to newer versions of FBA, but I honestly don’t think it’s going to happen, especially given how busy Ponder is these days.
//EDIT: I just tried the latest build of FBA, and it does seem like input lag is a lot better. Still not quite as good as ShmupMAME, but it seems like various fixes the devs have made worked as it feels more responsive.