Since Mustache is just a template language in JavaScript, you can do anything you can already do in JavaScript, and JavaScript is Turing complete. So no, there s nothing that you can t do in Mustache; in fact, there s nothing you can do in Mustache that you can t do yourself in JavaScript, it just makes some things more convenient.
When evaluating something like this, instead of determining what it can and can t do, it s more useful to ask "does it make the things that I need to do easy" and "does it make the mistakes I want to avoid hard to make."
For instance, one way to evaluate it would be whether it makes it easy to avoid cross-site scripting (XSS) attacks. According to the documentation "mustache.js does escape all values when using the standard double mustache syntax", so it sounds like it does do a good job of helping prevent these sorts of attacks.
To do a better job of evaluating it, you will need to provide more details on what your requirements are. What are you trying to do? What do you need to integrate with?
edit
Even after your clarification, it s still not exactly clear what you re looking for. Even restricting yourself to expanding a single Mustache template with a single view as input, you can produce any arbitrary string, and thus any arbitrary HTML by just give it that string as input.
If you re asking whether you can perform any arbitrary computation given a template and a view to render, then the answer to that is also yes, because Mustache allows you to call functions in your template, and those functions are written in Javascript, which is Turing complete.
But both of these are trivial answers; you can produce any given output by providing that as input, or you could do any given computation by using a higher-order section. As I said previously, what is possible to do with it is less interesting than what is easy to do with it, and what mistakes are hard to make with it.
I suppose one weakness, that may be the type you re looking for, is that if you need more power than the Mustache system itself provides, you need to pass those functions in as part of the view. Thus, you need to conflate the object that is being displayed with the code that will be used to display it. And if you remove the ability to to call Javascript from the views that are passed into the templates, then you do severely limit what you can do. Given the fact that these objects are known as "views", it seems that it s by design that you mix in the presentation logic with them; this is very different than template systems in which you allow the template to extract values directly from your model objects.
