Sorry I have to disagree with you, the transaction fees are based upon the 'cost' to generator to include the transaction. The cost is directly related to the amount of data needed to be included.
In the future there will be no 'hard limits' on block size, only the risk that the block will be rejected and orphaned by the chain as it is to large.
When a generator deciding what transactions to include, if the network is already profitable with very large blocks, (eg. 20mb+ as they have much non-currency data in them), then including very small 'currency' transactions have a minute cost. For example, 20,000,000 vs 20,000,010.
If the block chain is restricted to just currency data, there is much less incentive to improve the efficiency of handling large blocks data. Therefore the relative cost will be much greater... 500,000 vs 500,010. Therefore the transaction fees required for small amounts of data are likely to be higher on a system that only induces currency data.