Very nice! I was working on a similar concept, though more for streaming location data rather than GeoJSON (drawing mobile device paths, visualizing accuracy, etc).
I haven't gotten around to making an official blog post announcement but it's here on github for anyone who is interested: https://github.com/hungtruong/pinbin
cool hung, that's where geobin came from. A need to visualize geo data that we were posting from a mobile device to a server :)
I took a look and pinbin's data format would work on geobin if it were moved from the url parameters into the POST body, because we look for more than just GeoJSON, but it does have to be valid JSON in the POST body: https://github.com/esripdx/geobin.io#how-do-we-find-geograph...
We've been using it internally as a debugging tool for the Geotrigger Service (https://developers.arcgis.com/en/features/geotrigger-service...), which is a geofencing API & SDK. We can make a mobile device spit out location updates and see them mapped in real time, see what the headers and content of the POST are, and figure out what needs tweaking. We wanted to generalize it as a free service to allow others to do the same and also explore how else it could be used.
I haven't gotten around to making an official blog post announcement but it's here on github for anyone who is interested: https://github.com/hungtruong/pinbin