This was probably inevitable, but Robin K. Wilson is the first to do it: a calendar of events happening on the various social VR platforms, all in one handy website, vrevents.io:

At the moment, it only covers events on five platforms: AltspaceVR, Bigscreen, Echo VR, NeosVR, and Sansar. But I can see the utility of this idea as more platforms begin to post their events here, either automatically or manually. I think this is a great idea!