Oleg Terenchuk (litwol) is now developing the JavaScript Theming module. The five second elevator spiel: this will move theming from the server to the client.
The longer explanation is a bit more exciting. This module plans to abstract the core of Drupal theming into a javascript layer. This will allow a JSON feed to pass raw data to a browser to be formatted on the fly for display.
The implications are astounding, and I'm still wrapping my brain around the possibilities. For one, it could mean super fast in place load times, because Drupal doesn't have to mess around with passing everything around the theming system. An AJAX request could just ask for the data, Drupal sends it, and jQuery will format your list, table, teaser, or what have you. In its second day of life, it already works with messages (and item lists, I believe).
A potential problem I see might be that slower computers would see slower rendering times. But this is already happening with some jQuery-heavy sites anyway. The benefit would be most seen with faster hardware, but this is always true with cutting-edge technology. Everyone else will catch up soon enough.
In any case, I have a feeling that by this time next year, I'll be blogging about the killer combo that changed the world of Drupal and is sending ripples through the Internet: Embed Widgets + JavaScript Theming...
PS Come to DrupalCampNYC next month to find out more!