RE: I'm totally in the dark about what the impact of the "transition to Unified Interface" means to us
Hi Partner,
For existing Dynamics 365 users currently working with the regular web interface the new experience is a significant change and migration to this interface should be careful planned.
Firstly, consider the different use cases in your business. Each work-stream can have its own specific Dynamics 365 app and user experience so consider which aspects of the Unified Interface, including custom controls, can best be utilized for these requirements.
To gain familiarity with custom controls and other aspects of the new experience, you can take a closer look within your non-production environment.
Microsoft recommends an initial test within a development environment using a realistic user persona where Unified Interface is enabled prior to creating a parallel test app. After mapping out the key business activities needed to managed specific scenarios, a quick check will highlight any issues or gaps that will need to be addressed in the new UI.
For example, some functions and plug-in's that you currently use may not be supported in the new experience. The legacy Dynamics 365 contracts entity and dialogs are examples of this. When legacy functions and customizations are no longer used this represents an opportunity to relaunch Dynamics 365 with an uncluttered interface.
A further step would be to create a pilot app that is used by a small user group which has the essential functionality to handle specific use cases and generate some excitement by introducing the new capabilities.
Additionally, you can refer the article which describes User experience with Unified client Interface https://docs.microsoft.com/en-us/powerapps/user/unified-interface