OK, I see your point. But isn't that a temporary condition?? I suspect that what is driving demand for those liquids is for chemical feedstocks (ethylene/propylene). There are only so many plastics/etc. that can be made, so I would expect that demand to become saturated at some point, and more LPG becoming available. As you say, right now, C1 is almost a waste product, so available disproportionately cheaply.
That is why the notion of using C1 directly in diesel engines is so intriguing. I was (as I now see incorrectly) thinking that uses currently powered by diesel would have to switch to spark ignition to use CNG. If it can be used directly, that changes THAT "ballgame" a LOT.
I agree it will be temporary. But I am guessing it will be driven more by increased demand in C1 rather than a saturation of Natural Gas Liquids. NGLs are not as expensive to transport and the world begs for cheap plastic. Consumption is easy to climb with developing countries. Also we can keep the NGLs and build more facilities to export polymers.
C1 for transportation is going to increase. There is too great a difference in $/BTU.