the template language lacks a number of things:

  need elsif support

  need to figure out if we want floating point numbers as well as integers

  make sure we can deal effectively with variables that have the same name
  as keywords

  need the ability to pass arguments to an included template

  need a way to chain filters, like [%= link | url | html %], so we can
  ensure correct encoding of urls in html

  need an object type, so you can call into arbitrary c functionality from
  templates

  should arrays have a method that returns length - 1, for easier looping?

  it would be nice if [% and %] were not required around every directive,
  for example, in template toolkit you can do things like this:

    [% for elt in elements;
         print elt;
       end
    %]

  unfortunately, adding that ability requires a pretty big reworking of the
  parser.

correctness issues:

  include command needs to guard against recursion