We are informing about the progress of migrating to Ionic 5 in the tracker, you can follow this issue: MOBILE-3320.
As per tentative dates, we'll release a version of the app using Ionic 5 in June 2021 (this year). This goes in line with the european Web Accessibility Directive, so other than Ionic 5 it'll also include accessibility improvements. This release will continue using the 3.9.X version number, and it won't include any major UI changes.
After that release, we'll focus on improving the UI/UX for 4.0.