Currently, the shortcodes have a way to specify a particular category (e.g., cat_id=4) that can be used to filter the results. It would be great if any field could be used in this manner. The WordPress get_posts() function has two parameters that work like this, meta_key and meta_value.
$meta_key and $meta_value
(string) (optional) Only show posts that contain a meta (custom) field with this key and value. Both parameters must be defined, or neither will work.
-- http://codex.wordpress.org/Template_Tags/get_posts
It would be great to be able to use the shortcode like this:
[project id=1 field_id="formfields-2" field_value="2009"]