Apologies for brevity, noob here and just throwing out an idea in case it's useful (probably already covered somewhere, but I haven't got time to do all the necessary background research).
Suggestion: To make it more difficult for a malicious attacker to reap quick rewards by double-spending large amounts with a relatively brief majority of the network hashing power, introduce a hash workload that is proportional to the sum of transactions in a block (probably the sum of the absolute values, and a "proportionality function" could be linear or exponential). The motivation is to make it more difficult for malicious attacks to hash-power their way through a few large transactions. Obviously, there are costs in greater transaction delays (and fees?) for larger amounts (absolute value).
If there is original value in the idea, I can try to make time to follow-up with a better BIP proposal.