The proposed solution would involve the use of a hardcoded blockhash that would allow for blocks in a chain ending with that blockhash to not follow BIP65 until that blockhash. This would be considered a softfork as rules are added that otherwise make valid chains invalid. However, Todd warns that if not implemented carefully, this could act like a hardfork. He questions whether the chain up to the block immediately before the checkpoint is valid on its own or if it only becomes retroactively valid when it hits the checkpoint.