The functions setSourceGasPrice() and setRelativeGasPrice() can be updated by all transmitters.
If different transmitters would have a different view on the world, they might set slightly different values. Also they could compete on setting values. If transmitters would be premissionless they might accidentally or purposely set wrong values, which would mess with the fees and possibly result in griefing.
Perhaps have a seperate role for gas price updates. Or maybe have a selection which transmitter can update the gas prices.
Values from the next transmitter overwrite the values from the previous transmitter.