I Agree. But I guess that the Library of Congress (and archive.com and Google Blockchains) will also save a copy of the major blockchais, but not of every obscure altcoin. Some anthropologists and economists may find them interesting. But then you will have to thrust again a central authority, and the magic of the totally decentralized blockchain will be lost.
Another possibility when it's clear that another coin is surpassing Bitcoin is to "register" the Bitcoin blockchain in the new blockchain, just store into the new blockchain a copy of the current sha1. (Or a harder hash of all the blockchain, to eliminate the possibility of collisions found with faster machines.)
Another possibility when it's clear that another coin is surpassing Bitcoin is to "register" the Bitcoin blockchain in the new blockchain, just store into the new blockchain a copy of the current sha1. (Or a harder hash of all the blockchain, to eliminate the possibility of collisions found with faster machines.)