I think it's more about what it can't do than what it can. The main page claims that the templates are "logic-less". There's some benefit to that from a strictly MVC standpoint.
Yet another solution for a problem that doesn't exist...
All these do is make the PHP template SMALLER. It's still JUST as complicated. {{#in_ca}} is just as complicated as <?php $in_ca? x : y ?>, it's just smaller. Passing this off to someone who can only do html, it might make it slightly easier for them to read, but honestly if they can't figure out how to stay away from PHP tags (or understand the minimal amount they will need to to do front end work) they shouldn't even be doing front end.
I can't imagine investing the time to learn or switch unless it can do something pretty spectacular, missing something?
Edit: Although I must confess I like the name, new Mustache() indeed!