Hi,
I agree, as requested,
The wp_password field is used to limit access to a specific post through a password, when set up, the post changes from public to password protected just passing that field is enough in xmlrpc.php to set the post_password into the db and rendering the post with a password validation box.

This requirements comes from posting batches and determine which one would or would not be officially published, and in some cases keep restricted access to post to a reduced set of users.

In my tests, by adding 'password':'wp_password' to the definition dictionary it posted fine.

I think it's the only missing method in there too.

Thanks,