Yes and No.

Whenever we add a new setting to WordPress, my instinct is to make it opt-in for existing installations and opt-out for new installations. In other words, I think auto-update should be turned on by default for new setups (defined in `wp-config.php`) but be something you need to turn on for existing installations (i.e. after upgrading WordPress).

This is a drastic enough change to the way we currently do things that it warrants educating users and clients about what exactly will happen. But for new sites ... let's just turn it on and move forward.