Phil responded to my post with his own balanced analysis comparing GreaseMonkey and the KNX model for page augmentation/customization. I don't doubt that the KNX model is more powerful, secure and flexible than GreaseMonkey - my original point was only that it was evolutionary more than .... well you know.
Whatever mechanism you use to augment/annotate the page at the browser, there is only so much page real-estate to go around.
I upgraded my version of Xmarks, a Firefox extension that syncs bookmarks across multiple browsers and afterwards saw the following on Google's search page.
The blue icon is the extension's 'Smart Search', appending its own links to Google's search results page based on some criteria I know not what. It snuck onto my page.
Makes me wonder how many different extensions, GreaseMonkey scripts, and information cards/selectors are going to be fighting for those precious few square centimetres (even fewer square inches) of real-estate besides the search results.
How will the user manage these? Cards, if grouped into personas (e.g. I'm in shopping mode), could be useful.
Also makes me think there is a market for SAO - search augmentation optimization.