Yes, as what you said, basically, there is no need to upgrade bootloader, just setup ENV or CMDLINE to load different OS. But util our U-boot is stable and can fully support:
- Android OS
- DualOS: Android OS + LibreELEC
- DualOS: Android OS + Ubuntu
There is no need to upgrade u-boot again, as in current stage, our team was still work and test on it, so, before that, we just recommend our users to erase the bootloader on eMMC when upgrade new ROM.