it is true that you cannot update the code, though the neo before the yubikey 4 was still running java applets and they had already disabled the possibility to

it is true that you cannot update the code, though the neo before the yubikey 4 was still running java applets and they had already disabled the possibility to update the code by requiring the yubico private company key (they're still using java applets). the original neo let you decide of the key/write to the neo, etc. Thus they did not "disable it because of hardware", it is a choice of their, which they had already made for a year or two anyway.