Note that this long awaited improvement is all undone by a very significant oversight;
here is what is suggested the improvement does. Actually it doesn't work out like this. The task from plane made /imported into Planner Premium (Project Plan 1) don't feed into 'Assigned to Me' section of the none Premium Planner unified view. So guess what - you can't include them in you 'My Day' and you can plan out tasks from multiple sources into your day plan at all. It is no different to the way it was.
Here is what this post suggests it will do;
Streamlined and faster. First, you will notice a more streamlined and faster user experience with simplified navigation comprised of three main sections: My Day, My Tasks and My Plans. (True - but 'My Plans' you can find the tasks from planner premium, but you can't 'Add to my Day" with these tasks & there is now way to incorporate them in the 'My Day' view)
All your tasks in one place. The My Tasks view offers you a single place (No it doesn't - Tasks from plans made or imported into premium planner don't show here) to see and manage your tasks with intuitive filters and search capabilities, including the source of the task, so you can get to what matters most to you fast. This includes tasks from basic plans, premium plans (No it doesn't - Tasks from plans made or imported into premium planner don't show here sorry), tasks from Loop, tasks from Teams meeting notes and flagged emails.
All your lists, plans and projects. The new My Plans view brings what was formerly To Do lists, Planner plans and Project projects into a simplified collection of plans, making it much easier to find the most relevant and recent plans. (This is sort of helpful, but not worth the extra $10/month)
Please allow the tasks from premium plans to be able to 'Add to My Day' including for group members who do not have premium subscriptions, who simply need to tick off tasks shared with them.