I think it's far more important to have a meta templating system for "end user" applications. For example, lately I was searching for a wiki system. I rejected all systems which did not use Template Toolkit (because this is the only templating system I can handle). Things would look different if there was a meta template module.

And it's not strictly necessary to support all possible features. Conditionals, looping and variable substitution should be enough, everything else being optional, but still accessible via the meta template module if the underlying system supports it.