Nothing to see here, move along
This action has almost no impact on the "luckless Russians who bought dot-UK domains". They'll still have them and their DNS entries will still work. From that PoV, nothing has happened. These registrants won't be able to *change* their delegations or contact info or update their registratons because Nominet has suspended the Russian-based registrars who would be involved in those registry transactions. This is no big deal unless the registrants need to switch name servers or their UK domain names are up for renewal soon.
Besides, I doubt uk domain name issues will be a top priority for Russia's oligarchs and kleptocrats at the moment.
What is strange though is the lack of openness and transparency about Nominet's action. Who proposed this and why? Was it discussed and decided by the board? When? Maybe it's a side-effect of the financial sanctions and that's made it difficult or illegal to do business with Russia.
Incidentally Nominet say they had £100K invested in Russia and are offloading that. Hmm...
https://www.nominet.uk/an-update-on-ukraine/