Don't know about Echo, but I just jailbroke and wiped an Amazon Fire Stick and installed TWRP and LineageOS on it. The exploit to unlock the bootloader has been patched in the latest firmware, but I don't see the arms race ending any time soon.
That's awesome. I have some old kindle fires with lineage. I mentioned the echo because they have been iterating the hardware to make it harder and harder to gain access. For example, I have one[0] where they removed the USB port.
