Registration Limit: Close registration when admin-configured limit is reached

First off, this is a great module, much appreciated.

Here's a feature I'm going to hack together for my purposes for now but I think should be properly implemented in signup.

It involves a new field called "Registration Limit" in create/edit node interfaces.
Ideally, it would be a textbox where admins enter a number and when registered user count hits that number, it closes the registration for that node automatically.

Since the amount of registered users per node is already being counted to display "0 individuals signed up", one can combine that value and the Close Signups feature to implement this.

Something like:
$registered_user_limit = something like 45; // some textbox/integer field defined in node/add & node/edit

$registered_user_count = db_num_rows(db_query('SELECT * FROM {signup} WHERE nid = %d'));

db_query('UPDATE {signup} SET completed = 1 WHERE nid = %d AND $registered_user_count <= $registered_user_limit');

Thanks again for your time!