From a developer point of view, this would vastly improve QA for web apps that have UI. As a user, I'd really appreciate a text-to-speech UI that does not require a keyboard or mouse. Ideally, I'd like to see the same UI available for anything, as if asking another person to interact with computer for you.

Filling out job applications using my resume

Filling in a timesheet for meetings for the week based on calendar items. Categorizing whether it's internal or external meeting based on whether email addresses invited match your employer's domains, and which project it was for based on the title and description.

I could use it to fill out timesheets in Zoho, find a list of Facebook events that I'm actually interested in, and download forms from my bank. These are tasks I do often that the UIs make far more difficult than they need to be.