I just don’t see how it even achieves this. In my opinion, you are just introducing an additional completely arbitrary unit. There is no reason why it should track anything like transaction costs.
I also dispute the notion that there is such a thing as a bus that’s not full here. This may happen at the moment, as Ethereum is still in a very early phase. Once it’s a well-used network, there will always be a transaction with very marginal value waiting. Why shouldn’t there be? Why should there be a finite number of valuable transactions? It’s much more likely that there’s a power law of infinitely many, less and less valuable transactions potentially waiting.