One of the largest hurdles in my mind to increasing the number of full nodes operating is the startup cost related to downloading the blockchain. A similar but less important (in my mind) issue is the amount of disk space required by the full blockchain.
At Pruning the branches in Merkle Tree Nick ODell writes "[Bitcoin Core] was built on the assumption that you download and validate all blocks." In Would moving a transaction from an old block to a new one allow more pruning? Murch suggested that some assumptions be checked, and I think one of them was my assumption that it isn't necessary to parse the entire blockchain. Thanks to Murch, this question is intended to address that assumption.