In response to this, it was suggested that at least one checkpoint should be included to directly check the assumption that no 50k re-orgs will happen. Checkpointing only needs to happen during the headers-first part of the download. If the block at the BIP-65 height is checkpointed, then the comparisons for the other ones are automatically correct. However, many people would like to verify the legacy chain. This makes the change a soft-fork rather than a hard fork, as chains that do not go through the checkpoint are rejected, but no new chains are allowed.