Has anyone tried this working only in the United States? I feel like this would be easier as internet access isn't at a premium (you can always tether on your smart phone worst comes to worst). The United States also has lots of large clients and if you want a larger technical challenge you can always set up camp near their offices for a few weeks and work in house. On the non-technical side of things you can find any kind of environment you want in the US. Mountains, beaches, cites, etc. I know you won't get the rewards of traveling abroad but you get 90% of what the ideal is and you can always take some time off big projects and travel abroad if you feel like it.
This is coming from a US citizen who loves his country despite all the fucked up shit that it's government does sometimes, so maybe I'm bias, but I definitely think the life is possible.
I'm sure it's possible, I've travelled through parts of the US with my business mostly on autopilot. The higher cost of living can make it trickier though, part of being a digital nomad is income arbitrage (ie earning a US salary but spending it in a country where your US Dollars are worth a fortune).
It won't be the same as travelling overseas & experiencing different cultures though... part of the fun is returning to your home country after months overseas and seeing your home culture with fresh eyes. But it could be a good start.
I think you're overestimating the difficulty of finding WiFi & internet, though. I've often found better internet connections while traveling through Europe than in the US. But if you're a US citizen, travelling just through the US will simplify visa concerns, which helps a bit.
This is coming from a US citizen who loves his country despite all the fucked up shit that it's government does sometimes, so maybe I'm bias, but I definitely think the life is possible.