Is this something you might consider implementing, possibly as part of the Shared library? Similar to KeyTipService, but with a twist.
Consider this thread as a visual example. Since I'm working within a document (browser tab), and I'm now entering data into the text box. Also assume that the previous posts in this thread are other scopes that I want to toggle between for quick editing. Pressing Alt would highlight key tips for the previous post (numbered 1-3), and endering 2 would turn the second post into edit mode, and move focus there. Commands would decide what will be done when I enter 2, and possibly an exit command for the scope I'm currently in (Add a comment box).
I would imagine this could be quite benefitial to a lot of registration systems, where one is not necessarily required to enter data in a specific order, and Tabbing through controls would be way too tedious.
As mentioned in the initial post, quick navigation between documents using i.e. Alt + Shift + G would activate my GMail browser tab/document.