Well it's certainly an interesting idea, and would be interesting to implement so yes, why not (though with big warnings if you enable it, etc., to avoid any possible problems with Trojans and the like).

I think that encoding an URL to a plugin would probably be the best method (to contain the code, the barcode would need to be pretty big), in which case any type of plugin could be specified, which brings us back to possibly just providing a link to an .install file somewhere (as I guess plugins will have separate packages).

Part of the goal of moving to Qt was to allow Python integration, so it will certainly be possible to try this out.