[darawk]

In Ethereum, reversibility could have strict constraints. For instance, you could devise a contract in which the funds are held in escrow for 90 days, during which time a neutral third party may reverse the transaction using their key.

The important point is that the actual parties to the transaction may choose how they want to mediate this, whether they want reversibility, what conditions they want it to have, and have it all enforced by code and cryptography.

Of course, this burden would only really take place on high value transactions. For most transactions, there'd be a standard configuration people and merchants would use.