The changes apply to: Customer Engagement online
Application owners and administrators should be making plans to move to the Unified Interface now. Whichever your approach, either a big-bang move of your main application or an incremental introduction of new apps on the Unified Interface alongside your main legacy web client, you should be using the Unified Interface entirely by October 2020.
"Microsoft's goal is to make Unified Interface the primary & only client infrastructure, all product roadmap investment is only there."
Now is a good opportunity to revamp your user experience!
For more information on how to transition to the new UI please contact your Account Manager or Service Delivery Manager to get the support you need.
Microsoft has provided the answers to many FAQs you may have: https://docs.microsoft.com/en-us/powerapps/maker/model-driven-apps/faqs-transition-unified-interface
Moving to the Unified Interface shouldn't be seen as a burden. There are many reasons we have seen why it is better than the legacy web client.
It's modern, the web pages flow and respond to different sizes and devices - in fact, it's the same interface on web browsers, mobile devices, embedded within Outlook - so it's just so much fresher and now consistent across devices which aid end-user adoption.
It performs better too on modern browsers, much better. That's so important and allows for much more graphically rich and interactive web forms. The Unified Interface brings modern components which engage end-users: graphical controls, interactive widgets from the PowerApps Component Framework and Microsoft's own re-thought layout and command buttons.
And with the model-driven app concept, it's a great way to build apps-for-purposes instead of one huge app used by everybody. Yes, the back-end is the same but end users can be more engaged with tailored apps for them.
This genuinely is a time to re-think how you want end-users to engage with the apps.