Velojet, the tool and the method I described does indeed provide an add-on where users would only need to do a one-time install, of their particular C2 project. It's on a per-game basis.
The type of plugin you're describing would likely allow for the uploading of any C2 exported project and would then make it easy to include the project in a WP page. It's just a different type of plugin, though they're both technically plugins. The use cases are just different.
The plugin I'm talking about here allows a game developer to make their single project available very easily to the WP community. For instance, if someone made an alarm clock with C2, they could package it up in a plugin so WP users could use it on their site.
With an exporter in C2, it would be that much easier for the developer to achieve. And this is very useful for game makers wishing to make their games easily available to the WP community.
I'm not at all saying this needs to be done, an exporter like that seems likely to take a bit of time away from C2 developers. I'm just saying, if anyone's interested in making such an exporter, I'll gladly assist however I can.
That said, it's possible to make a plugin that lets users upload their C2 projects (likely best done by uploading a zip file), at which point the plugin would provide an easy way to use that project. I've been considering how that could best be done, myself. However, I'm also having a hard time seeing how that would be as useful unless someone was intending to open their very own arcade site (a broader market).
On a side-note, in case you're not familiar with it (I've met quite a lot of folks who weren't aware of this one), WordPress can now use particular embeds without any additional plugins.
More on that here: http://codex.wordpress.org/Embeds