Web Intents is a general Service Discovery mechanism and Web Applications should not only be able to discover and use Web Intents Services in the cloud but also local Services.
An addendum specification to Web Intents defines how Services on UPnP and mDNS enables devices in local IP sub-networks could be discovered and used by web applications:
Below is a presentation based on a simple use case "Play video on remote device" that proposes different Web Intent based implementation alternatives for discovery and control.
Below is a link to a video of a demo for the use case above.
Also see wiki page TPAC 2012 session on Web Intents and Web Intents for local services
Claes Nilsson, Sony Mobile Communications