What if Bitcoin was reimagined today, under modern cryptographic assumptions, using a principled minimalist architecture designed for long-term auditability and zero-trust adversarial environments?
If Bitcoin was reimagined today, I guess it wouldn't be as decentralized as it is right now because reimagining means governance and central decisions taken on the coin. But lots of things would change. I think that today, reimagined Bitcoin would be quantum resistant. I think that it would have more energy-efficient consensus than Proof Of Work is. Transactions would be either more anonymous or they would be left the way it is now but I'm sure that the fees would be much lower and the block size would double after every halving or it would be flexible, the whole system would be designed in a way to prevent miners and spammers to abuse transaction fees and to get rid of unwanted block size to make running a Bitcoin node easier and accessible for many people.
I'm sure that lots of things would change but it's hard for me to speak better about it because it requires knowledge of programming and cryptography.