It's simply privileging calldata with lower gas (changing a constant) plus adding a cap on the maximum amount of calldata that can be in a given block to prevent crazy state bloat. It's effectively baking in L2s as something the protocol wants to encourage by giving them a "tax break". Note that the gas market is still in effect, so this is "tuning call data against the other costly aspects of ETH tx processing" rather than some "magic price reduction".
