Hard to see altcoins adopted because a city like Miami even created its own coin. It's an example of the adoption of an altcoin but not really the existing one.
Bitcoin will be more adopted than an altcoin because it's more popular and it's a store of value as a use case. Other altcoins has its own use case for their own community. Today we still consider altcoins as shitcoins.
You're right, for Bitcoin will be more of a more liberal system of legal payments within a country, Maybe altcoins don't play that wide role. Miami has not fully implemented the concept in a comprehensive way, but it is possible that Miami can implement all of it smoothly even though it requires a process of public acceptance and support from the government that really wants Bitcoin adoption.