Google have already made some progress towards adding extensions to
Chrome -
http://www.mattcutts.com/blog/write-chrome-extension/
This probably isn't much use right now as it has limited functionality
and only works in the dev version of Chrome, but it shows that they're
not far off an initial extension feature.
Even if the first version can only do Greasemonkey-like stuff, that
should probably be enough to do what the Zemanta bookmarklet is doing
now.