This is one of the most important and hotly debated questions abotu the new parser design: should it allow syntactically incomplete templates, or not?
Yes, it's got all sorts of wonderful technical advantages: a DB-less translation from markup to DOM is nothing to be sneered at. Though I can throw out this cautionary tale: our old MW parser implementation didn't allow these "partial" templates, and our writers have spent maybe a dozen hours fruitlessly trying various crazy ways to factor up collections of common bullet points for use in lists of instructions.
Cheers, Erik