No, it's not about trading of account claim tokens.

Rationalization here means that accounting for RC costs will be charged more realistically (more rationally) based on their real costs to the blockchain. For example, one of the dominant factors in terms of CPU consumption for processing an operation is checking the cryptographic signatures that were used to sign the transaction that contains the operation, and this cost is independent of what the actual operation is (and instead varies based on how many signatures were included). But previously the cpu costs for checking these signatures was ignored.