I have implemented an HTTP data broker integration with ThingSpeak. There seems to be a large amount of public IoT data available and it should be possible for anyone who wants to use their service. There is a slightly different naming convention on ThingSpeak from what I have noticed some other brokers using. ThingSpeak seems to use "channels" and "fields" where other brokers may use "devices" and "topics" respectively. Where the DataGator service just makes different aggregated topic level data available.

Some broker integration has also been done with OpenSensors. This integration has proved to be more challenging as there is more variety in the way the data is structured on the broker. This variety in the data storage structure made it necessary to construct different parse paths into the structures to allow describing where exactly the data of interest is.

I think the DataGator will complement with what the brokers offer. The visualizations that are provided by ThingSpeak seem to use client side JavaScript and what the DataGator service would offer are rendered server side. Using server side rendering should provide an advantage for constrained clients and make it easier to directly display visualizations on these devices.