Perhaps, but I'd counter that with the trip I just planned I didn't need a tool to do it. I shared a google doc with a friend for one and had a couple skype calls. For another I just went over to her house and we figured out the dates, where we wanted to go etc. Her roommate might come now, as a friend whose in London. That is "social trip planning" but I'm not sure what framework, and there are a bunch out there, could help make that easier. A lot of it is serendipity based, and the logistics weren't that difficult in the first place.