I like to provide a custom template for displaying my notes. I find that being able to add an extra bit of styling and logic make the UI sing. 
Kudos for giving us that level of control. 
Some of the features that the default display are able to render cannot be replicated with the current tools. I’m thinking of lookback links in particular.
This morning it occurred to me, as I renamed “display.html” to “_display.html”, that being able to switch between the default display and custom display would be a nice addition.
I think it has a level of utility that goes beyond the reason that I’m asking. As soon as we start using display.css, display.html, or custom.html for classes, being able to switch quickly between a custom display and the default display is generally useful.