In #56817 the ability to preview the template of a post right in the Post Editor. This is a really nice update that is a huge win for making the editor look like the frontend.

Ideally, I would love to be able to have this turned on by default. Either as a user setting, or even a global option that could be applied via a filter somewhere.

Another option would be for the setting to simply get remembered so that when you enable the template-locked rendereing mode and for example reload the editor the setting gets remembered. Kind of like the code editor vs. visual editor setting gets remembered.