Seriously doubtful that .io will go away. More likely that a registrar will take over it as a generic TLD, as there's a lot of money to be made.
.gb and .uk are both for the same country. Also .io is associated with that country as well. And politically. .gg and .je also belong to the British. Those two are not even countries to begin with. They are "crown property".
And since no .io domain ever was registrated to anyone living there, on account of the area bein non inhabitated (by civilians) before the internet arose, the domain registration in this case was dubious from day 1. For all intents and purposes it was used as a general tld from day 1.
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Oh, and the nic for io is this one. And they also do .ac and .sh, two more British tld.
Internet Computer Bureau Ltd (ICB) is the country code top level domain manager and registry operator for the .IO, .AC, and .SH top level domains and is located in the United Kingdom.
None of those are the same country. They are distinct countries.
And the gb / uk thing exists because of the northern ireland situation. Its an exception and a very old one and gb does not refer to uk, but uk does include gb.
Each distinct political area has one tld.
While .io might not have been registered by an inhabitant, the country code it is sourced from WAS used by people living there and continues to be used officially today.
My point is, they should not try to enforce rules they did not enforce in spirit previously. That they even allowed the .io tld to be used at all speaks volumes. It was never used as a country tld. It was always used for people and companies not living there.
Iso country codes are one thing, but top level domains are an internet thing. They could just as well have designed it with the 3 letter iso country codes. That is even more techy. Internet of Things. .iot And Ireland would have .irl which would be very popular I guess, as it also means in real life. Or they could have used any other design for dns and country specific name resolving.
What they did use is the 2 letter iso codes wherever possible and refused to allow 2 letter tld to reserve for new iso codes. But that code is burned in iso. They will not re-use it for another country. So it is free for usage as a general tld. We shall see how sensible they will handle it. Could turn out either way.