I will have to correct myself. Looks like pre-order is working. The problem is the ec_add_to_cart_link proc.
This query :
set available_date [db_string available_date_select "select to_char(available_date,'Month DD, YYYY') available_date from ec_products where product_id = :product_id"]
Should be :
set available_date [db_string available_date_select "select to_char(available_date,'Month DD, YYYY') as available_date from ec_products where product_id = :product_id"]
NOTE : that the first query is missing an "as" before aviailble_date.
This fixed the proc and now shows a "Pre-Order Now" button in the product page when Pre-orders are enabled in the ecommerce parameters.