When a new front-end app is created, there should be a prompt for choosing the whether the app should include both, a light version of the default theme as well as a dark version of the default theme. 

Along with this, a page template can also be added that provides a built-in toggle feature that toggles between the two themes (a page layout perhaps hosting the theme switch implementation).

Rationale: This helps app developers build multi theme app (typically a dark and light theme option) out of the box were only the specific elements of the theme be customized by the theme developer