The proposed alternative is to hardcode a blockhash which will exempt a blockchain from following BIP65 rule up until that blockhash, while any other blockchain without that blockhash must respect BIP65 for all blocks in the chain. This would be a softfork, as it only adds rules that make otherwise valid chains invalid, while still allowing large reorgs under stricter rules than before. The term "exemption hash" is suggested to denote the hardcoded blockhash.