AFAIK Samsung and Xiaomi only blocked BL unlock recently, so IDK what you mean by the 2014 (if you are referring to Odin and MI unlock tool then its a valid point)? Also, if I understand the EU RED and the recital 19 correctly, the device shouldn't block the firmware if it is compliant with RED to facilitate competition. If the ROM doesn't allow to surpass the limits imposed by the standards, then the device should allow you to use that said ROM.