Anything that's either going to be taking in a large amount of relevant data (such as GPS applications) or has an installed userbase large enough to warrant inclusion in the "big names" that I specified above. It doesn't have to be major companies but there has to be enough data to make contributing to it worthwhile. It's kind of a catch-22 that is solved by either industry wide grassroots acceptance or a big name player coming in and providing the initial data.

To use my previous example, if Google dumps most or all of it's map data into this endeavor it gains a tonne of legitimacy. Otherwise your just a little fish in a big ocean of data that people are holding on to and refusing to share.