Completely block access to WP Admin Dashboard

Seeing how WordPress is evolving on the market and developers are pushing more CMS based themes allowing front end user postings, shouldn’t this option (blocking access to the wp dashboard be available to turn on/off pending on the admin’s choice?

The strongest and most effective way I found to complete such task so far is by adding the wp-admin restriction code in functions.php yet sometimes it blocks access to some Ajax calling used by some plugins which breaks them and makes them obsolete.

Really wished they would introduce this kind of option in future releases.