Why would it be moot? I do something similar to this technique with haml-js and underscore templates (though i wear a full beard, i'm not really into mustache.js)

This lets me use the same views on the server and the client, with the same $templates.render("item", context); where "item.html.haml" is the name of the source file. I pre-compile the source of all the .haml files to functions and add them to the $templates object (boo, globals, yadda yadda yadda) and then write this out to a file for serving to the browser (./public/templates.js by default.)

Then, when I make a json call or whatever and need to re-render a partial, i just call the same template rendering.

Note that this works for Node.js but you could easily make it work with ruby through redcar or use a similar technique for precompiling your mustache templates for the browser while still using your language-native implementation on the server.

Edit: forgot the link https://github.com/aaronblohowiak/shared-views