Much has changed since I posed this question in 2021. SwiftUI has matured considerably. Most of what was missing has been added. Much of what was flawed has been fixed. 

Remembered for iOS and Remembered for Mac have been rewritten almost entirely using SwiftUI (I dip into UIViewRepresentable a bit, but only to support some unique/non-standard UI implementations). Both the mobile (iOS/iPadOS) and Desktop (Mac) versions are stable, with no crash reports. 

The advantages of SwiftUI are abundant, and covered elsewhere extensively. Don’t want to discard all that time and effort you put into learning UIKit? That’s how it goes. I don’t remember much about coding in 6502 assembly language either. 

Just embrace SwiftUI and don’t look back.