So, my two cents: no. Any application that's useful can be integrated into MediaWiki itself, or a toolserver tool, or a client-side program with access to the password.
Client-side as in a desktop application? How is that any different? Couldn't an evil desktop app send its passwords off to its evil author who then uses them for evil purposes?
To emphasize this point, the desktop application could also use OAuth, which would avoid this issue as well. Also, you'd then be able to limit the actions of the desktop application as well.
V/r,
Ryan Lane