I just got my Fire 8 2022 last week and it was running 8.3.1.1 out of the box. I took the plunge and updated to 8.3.1.4 since I could just exchange it if I wanted to start over. I am able to install the Play Store and disable system apps even with the latest update. I did disable system updates after that.
One thing I have noticed is with Gboard and perhaps other Google apps. Even after updated Play Services, I get an error that my devices must have Google Play Services to run Gboard. I eventually got it to work, but I continued to get that notification.
Thanks for posting. I had done the same myself, but hadn't got around to posting the results. As you said, you can still disable system apps with 8.3.1.4 but the minor issues I have had with 8.3.1.3 have not been fixed: you can't sync your bookmarks with a recent version of Chrome, though you can get around this by installing a version from a couple of years ago (Chrome 81.0.4044.138 works), syncing, then updating to the latest version. Though the update will stop any further syncing with Chrome. Also, recent versions of Google Calendar crash while trying to complete setup: Calendar_2020.40.1-336039884-release works, but cannot be updated. I downloaded the old versions of Chrome and Google Calendar from the Uptodown appstore.
I have not found any advantages to the 8.3.1.4 update compared to 8.3.1.3 and one minor, but annoying disadvantage. If you disable system apps that have desktop icons, e.g. Amazon Kids (com.amazon.tahoe) the icon disappears from the desktop, but appears again a while later, though the app is still disabled.
