I'm not too sure if we should be adding too much logic in the templates (gets super messy). That said, there is a way for you to accomplish the above, via helpers.
JS:
templates.registerHelper('iterateFn', function(data, iterator, total) {
return (data.someVar && iterator === 3) ? true : false;
});
Templates:
<!-- BEGIN someLoop -->
{function.iterateFn}
<!-- END someLoop -->
Some real-world examples found here (none using the iterator variable as of yet though)