There have been many articles that state that hosting data on a 4G network is actually cheaper for the carriers because of the speed. Less stress on the network because it gets your request done faster. I wish I could find the link, because now I look like I'm talking out of my ***. It was Verizon that said it, I think.
It will cost Sprint less to deliver a GB of data over 4G then 3G but it will still cost more to deliver 2GB on 4G versus 1GB on 4G. AND, the rate the data use is increasing is MUCH faster than the bandwidth that 4G offers over 3G.
But, as I said before, sooner-or-later this will be resolved when the carriers switch to metered billing. That way it won't mater what you do with your phone they will still get there money from your because the own the pipe and can know exactly how much data you use. So, even if you root so you can get the hotspot without paying for it they will still get you because of the data you use.
There is no free lunch so the carriers expect to be compensated more when you use it more. The current billing schemes do not take into account the fact that many have found a way around the fees they impose for things like the hotspot by rooting.
The early days of music downloading had only a handful of people doing so but as the software for sharing and downloading became more available and powerful the number of folks, with little or no tech experience that were getting there music by sharing/downloading increased to the point where the music industry is now on the verge of going out of business. The carriers are no doubt aware that rooting makes them vulnerable in a similar way but they have an Ace in the hole the music industry doesn't have -- they own the pipe!
Going forward the carriers will have to evolve the cell network to increase bandwidth for the ever growing number of smart phone users that all have an ever growing demand for data. Since the max bandwidth for a given cell/antennae is pretty well fixed the only way to increase bandwidth in an area is to increase the number of cell/antennae locations and run at lower power. As you can imagine that wont come for free so the carriers will need to be compensated for it or they will have only two options: throttle service or go out of business.
I foresee the day when a 5G or 6G network consists of many times the number of cell/antennae locations with office building have there own cell/antennae setup and likely many. That way the number of users on each cell/antennae can be kept to a lower number so the bandwidth isn't spread too thinly.
So, getting back to the current topic, the switch to metered billing will make the habit of streaming music and/or video and downloading large binaries very expensive so perhaps it would be wise to avoid developing those habits in the first place. I for one have 16GB of music and I carry that on my phone at all times so that I don't have to waste bandwidth streaming. It may not matter now with unlimited data but, as I said, when they go metered the habit of eating GB's per month for something you can easily avoid will prove unwise.
Brian