The throttling down in speed past a certain data quantity limit is the big gotcha in the so-called "unlimited data" smart phone plans.
What we RV'ers need - and I'm sure the providers are aware of it - are affordable plans for cell tower based (or even satellite based) Internet appliances that are like the wireless Internet service we have broadcast to our residence here in the mountains - unlimited data with no slowing of speed (throttling). Our home Internet access - always on with no data limits - wireless Internet service (not cable, cell tower, or satellite based, by the way) is around $72/month and is fast enough so we could stream video continuously if we wished.
I'm guessing ... but it will probably take the new upcoming 5G cell tower based Internet service to provide this affordably across the U.S.. But it probably will be introduced into the town/cities first ... and later out into the rural areas and boondocks (if ever) for us drycamping RV'ers.