Updated without too much problem. The first boot into the installer gave an error (correct updater resources not available or something), but rebooted again into the installer and it seemed OK then and seems to have installed fine.
Best part is that I have been able to turn off RadeonDeInit (set to false) and my MSI RX 560 GPU (dual 2560x1440 screens, DP and Dual-DVI) is working fine. Still early days but running a few benchmarks shows performance is fine (as before). Seems like native support has arrived for quite a few more graphics cards.