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Most cryptocurrencies are spec'd to stop creating new coins after a period of time. But that doesn't mean one couldn't design a coin where inflation is controlled by an entity with the right key.

Even without that consideration policy changes can be enforced by Software updates. In the case of bitcoin gridlock has stalled this process but other coins have managed fine. The government has a strong compelling argument to force upgrades - you can't pay your taxes if you don't and then you will go to jail.