if the data transfer is done from the client (and i bet it is, as it's much harder to persuade people to run code on their servers) then ghostery and the like still work, because they block the transfer (since the code to do the transfer must be loaded from the weasel site - same origin policy).
+-------+ +----------------+ +------------+
|Browser|<==A==>| Visited server |<==B==>| ID service |
+-------+ +----------------+ +------------+
The client data acquisition is done through A (AJAX), then that info is sent through B (API call) to get the identity. The browser doesn't interact directly with the ID service.
The data acquisition scripts would be served directly by the web sites.
