There's finally a discussion starting about the idea of the Library of Congress archiving Twitter among librarians. That's good. I want to provide some more food for thought.
First, I think there's general agreement that we like to support the open web whenever possible, and if there was a thriving alternative to Twitter that wasn't owned by a single corporation, that would be something we'd like to see.
However as time goes by, the advantages that Twitter (the corporation and its product) gather make it harder, and less likely. It's good that the corporation is cooperating with the Library of Congress, but with the open system there would be no corporation whose cooperation is required. And because there's no corporation, the support of public institutions is even more important.
Now here's the funny thing -- Twitter is already competing with an open system -- the blogosphere. It predates Twitter by about a decade. And the archive of the early history of the blogosphere is fading away, like an endangered species. Twitter's archive appears, for now, to be safe.
With Twitter there's a rich corporation minding it. They can and imho should be funding their own archive. But with the historic blogosphere, dating back to the early-mid 90s, a lot of it is already gone. The need to preserve it, by independent historians and librarians, is greater and more immediate than the need for Twitter to be publicly archived. (And why should US taxpayers foot the bill?)
So it's a matter of priorities. I have no problem with the public investing in preserving a historic archive of Twitter, as long as we preserve the open stuff first, especially the blogs that led to Twitter. How innovation happens is something that's much debated. But here we have a unique archive that actually shows how innovation happened in a very important area. To lose that would be to lose one of the most important things created in that timeframe.
I feel very strongly that we should encourage open alternatives to Twitter to develop, and right now the LOC is actually discouraging it. That's not consistent, imho, with the mission of libraries, and especially not consistent with the mission of the US government's main library. I say that as a vocal citizen, voter and taxpayer, and as a lover of history and technology.