Some people see it that way. And it probably does serve that purpose to some extent in areas with very unstable governments, like some developing countries. But I'm doubtful that by the year 2121 Bitcoin or any other cryptocurrency will have kept the US government "in check" in any way. It's not impossible, but I'd heavily bet against it.
They may very well make/adopt some cryptocurrency as the new primary fiat by then, but I kind of see the idea of Bitcoin keeping the US government in check similarly to the idea of gun ownership keeping the US government in check.
Out of curiosity, can you describe an example of how it could potentially serve such a purpose, even in a hypothetical contrived scenario?