the language lacks a number of things:

  if/unless statements need to support ==, !=, >, <, etc.

  figure out how boolean evaluation of scalars should work

  print should let you index into an array

  include/process directive, to pull in either files or templates

  ability to use quoted strings/literal numbers as args

  need elsif support

  decide if we need the ability to modify variables from templates, given
  the problems with memory allocation this may not be worth the pain

  consider splitting string and numeric variables into two types, since it's
  easy to allow modification of numbers because they don't change size

  need a data definition language, to allow you to easily specify a set of
  variables, like hdf in clearsilver.

the command line tool has a few other issues:

  should be able to define arrays and hashes from the command line

efficiency / correctness issues:

  we need to produce useful error messages not just return APR_EINVAL