The UART console does not depend on firmware. This is a special additional hardware USB-UART, for connecting to another device, details are easy to find by the keyword "UART console". The UART console allows you to get detailed data about the startup process and is needed when something is not working ( in your case, to analyze what is causing the problem in the new firmware 9). But if you go back to the previous firmware, everything should work again without the UART console.
Yes, I was forced to change the version so that the system would not be confused when analyzing (the semantics of analysis is a larger version, so it is a newer kernel, if there are two packages with the same name, it takes the first one).
arm-64-current aml-s9xxx-current ... rk and alwinner This is the same core.
The DEV version is "clean" NEXT kernel from GIT Linux (without additional patches). It changes very quickly and there is no point in releasing it as a separate package (I only collect them as part of the image for quick testing of new features).
Support for network repositories is handled by @Igor, so it is better to ask him this question. As far as I know, this requires a lot of space to place and time to keep up to date.