I've been using GBP for the past month or so, just for ginger beer. My kids love the stuff. It may be that it wouldn't thrive quite as well with other ingredients, but if you kept the acid level about the same, it should at least work to some degree.
i have also had my gbp about a month, have been kind of blindly testing different recipes and so far it is gangbusters with whatever i put in there (different sugars, lemon/lime, chilis, varying amounts of fresh ginger) so i will eventually try some lemongrass and report back. the only thing i have challenged the gbp with that has word-of-mouth antimicrobial properties is the chilis, and those didn't seem to hold it back at all