When it really truly matters, like when I have a business need to download huge items in remote areas, the $10/GB+ justifies itself.
And video streaming, probably most people's biggest bandwidth use, fits very well on phones.
Does anyone offer a tethering plan that's rate limited but not data limited?
T-Mobile in the US; they give you a set amount of high-speed tethering based on your plan, then it rate limits severely until the end of the billing cycle unless you upgrade your plan or buy a a pack of data.
Though with how happily and loudly they've made 1.5Mbps video excluded from data caps, it would be better if the throttled speed was at least 1.5Mbps.
My problem with this is that it's the wrong measure.
There's no good technical reason to shape traffic to a specific rate irrespective of network conditions or capacity. All of the links in the chain support QoS.
Shaping a bandwidth hog to a tier below the rest of the users makes sense, but that's not what's going on.