I don't think it would only reach .1% of their population.

It's talking about replacing all of the Twitter accounts of government agencies with accounts on a central mastodon instance for the government, that would serve the same "information broadcasting" purpose. I'm not talking about people having to create mastodon account or choose an instance or even use mastodon.

I think far more than .1% of people can read a public mastodon feed for information from their government

The very fact you need to create an account on twitter to view tweets should be a blocker for any gov't communication. That twitter rate-limited views is another strike against them. Government information should be open access. I don't know if activitypub is the answer, but they need to get off twitter.