Templating engines are a dime-a-dozen right now, ranging from micro-DSLs to opinionated behemoth frameworks. It can be a bit of a chore to wade through them all (even with a Template Chooser), and even when you settle on one to use, it may not have all the functionality you want. So what do you do? You write your own, with as many custom and customizable features as you wish.
But writing a templating engine can be a whole mess of a problem all by itself. Writing a custom DSL that won't break with a mis-placed space or capital letter, and does what you want it to do, and ready for future changes, improvements, and additions, is just a pain the behind.
So what would the ideal-world, blue-sky apex of templating engines look like? What would you be able to do with it? If we're talking about JavaScript and HTML (and in this article, for example's sake, I will be), you'd want to be able to use all the power and simplicity