In theory, version 3 of the Stack Exchange API will allow posting to the system. Announcing API version 1.1 and RoadmapAnnouncing API version 1.1 and Roadmap (includes a roadmap of the future of the API)
I expect at that point you'll see all sorts of plugins that allow one to view topic specific widgets, and post to the sites on the specific topic assuming one is logged into the stack exchange network.
Until then, I would expect (and hope!) that SE Inc spend more time bringing the API forward than trying to make and maintain widgets.