There are people in this discussion suggesting that someone who doesn't want to comply with such rules can go **** themselves and just give up on entering the US market. Well, guess what? They probably would. The burden imposed by this kind of requirement would almost certainly be prohibitive in cost. A vendor such as Microsoft would therefore do better to sacrifice the entire US market if it meant avoiding both an eternal unfunded mandate to support everything they ever sold and giving up their trade secrets to all their competitors.
It's more likely that they'd make Windows subscription-only, charging by the month or year, with a feature that causes your product to stop working if you don't renew your subscription. Which for an OS is crazy, but that's the incentive this requirement would create. Microsoft might even prefer this business model, but would never think they could get away with it, unless there was a rule that essentially mandated it. And perpetual free support would pretty much mandate perpetually charging for a product.
How this would relate to XP EOL is that they wouldn't renew any licenses for an OS past it's expiration date, and when the terms of your license agreement explicitly state you can't use the product, they can't be forced to support it any more.