There's two issues here; a delay before Roslyn sees the changes, and the requirement that you need to switch pages to see changes
The need to do the page switch is, because when the control comes back to the Property page, the page is refreshed, At this point, the Design time build is done and the list gets refreshed to the correct value.
With your change, if the imports list change were pushed to Roslyn Workspace through evaluation then the change could reach faster. Hence the page refresh that happens at the end of UI operation could get the updated list. This eliminates the need to do a page-switch. Of course, pushing the change to Roslyn Workspace could still be not fast enough. At that point, we will have to look for other ways to make this work.