Since Amazon's Fire HD 8 (2018) runs Android 7.1 Nougat-based Fire OS 6, being able to run Android 10 on this slate is definitely great news. Obviously, this is only possible thanks to a third-party ROM — namely LineageOS 17.1 — which is already available for those eager enough to try a work-in-progress piece of code.
https://www.notebookcheck.net/Android-10-based-LineageOS-17-1-available-for-the-Amazon-Fire-HD-8-2018.483268.0.html