In the latest developer's build of the game, we've implemented an "Unassigned" option to the list of commands available for L3/R3 (Left Stick/Right Stick). We'll be implementing this in patch 2.1, so please hang in there just a little while longer.
In Regards to Implementing Features Ahead of Patches
We've been searching for a method to release features like this (and the sort feature) as quickly as possible. However, because the official version of the game and the internal developer version have various differences, it would require individual checks and implementation on both versions to release specific features ahead of time.
As the number of features we implement ahead of time increase, there would consequently be an increase in the amount of time needed for checks as well as transplanting work to be done. Due to this, the number of features we can implement by the patch would be reduced.
With that said, we've opted to introduce features where the risk of implementation is realistically manageable and the effects of addressing it are high to be implemented ahead of time.
As a player myself, I understand your feelings when things are inconvenient, and I apologize for this.
The ability to turn off the Lock On feature has comparatively less related features associated with it than the item sort feature, and is a feature that would be easy to implement ahead of time. We'd like some time to looking into whether we should implement this ahead of time with other important features such as the pet and minion targeting adjustments and RMT blacklisting.