[DrJaws]

you won't forfeit the domain if you are a EU citizen no matter where you emigrate.

The domains are for residents on the EU or EU citizens. That were the rules when people registered them. As UK left the block and are not EU citizens, it's not spiteful nor petty, just the rules they accepted when they decided to register the domains

[hanoz]

You will if you take up citizenship in a country which doesn't allow dual nationality, or, more commonly, you will if you're an EU resident who doesn't have EU citizenship.

It's a bad enough rule to apply to individuals, but to apply it on mass to people, probably most of whom didn't actually want to leave, of course is petty and spiteful. You can be on either side of the Brexit debate and see that. Where's the good will?