Associating a Theme with an App Module would have multiple benefits:

• Better User Experience for companies that have different Business Units with multiple identities and that use a single CRM instance.
  That way, each app would lead to a custom logo & color theme.


• More powerful demos for pre-sales who could be able to customize a single instance of Dynamics 365 for multiple potential customers. That way they would only need to customize Apps to offer a differentiated experience.

The App Designer (https://....crm.dynamics.com/designer/app/...) component should let system customisers select a Theme.

To facilitate things, it should be possible to integrate Themes into solutions, for better Theme GUID deployment.