I can understand governments wanting this to be an option but I would let them do blocking within their countries to their own people if that is their desire. This is another pandoras box. Its bad enough that some countries control this already to block free flow of information.

This will not stop Russia, they will just run their own state sponsored DNS servers. We can imagine what else might be implemented on that concept...
Countries or users that still want access will do the same with custom DNS servers.
This will take us down another path of no return as a global standard that is not political or politically controlled.
The belief that the internet is open and free (as much as possible) will be broken in one more way.
This will also accelerate the advancement of crypto DNS like NameCoin (Years ago I liked the idea but I don't know how it is being run anymore.) or UnstoppableDomains for example. Similar to what is starting to happen to central banking as countries start shutting down bank accounts for political reasons.

I don't like the idea of disrupting any Internet service. But the current situation is unprecedented.

The Achilles Heel of general public use of Internet services has always been the functionality of DNS.

Unlike Layer 3 disruptions, dropping or disrupting support for the .ru TLD can be accomplished without disrupting the Russian population's ability to access information and services in the West.

The only countermeasure would be the distribution of Russian national DNS zones to a multiplicity of individual DNS resolvers within Russia. Russian operators are in fact implementing this countermeasure, but it is a slow and arduous process, and it will entail many of the operational difficulties that existed with distributing Host files, which DNS was implemented to overcome.

The .ru TLD could be globally disrupted by dropping the .ru zone from the 13 DNS root servers. This would be the most effective action, but would require an authoritative consensus. One level down in DNS delegation are the 5 authoritative servers. I will leave it to the imagination of others to envision what action that could be taken there...

ru nameserver = a.dns.ripn.net
ru nameserver = b.dns.ripn.net
ru nameserver = d.dns.ripn.net
ru nameserver = e.dns.ripn.net
ru nameserver = f.dns.ripn.net

The impact of any action would take time (days) to propagate.