[jstanley]

There are several potential paradigm shifts which this doesn't address.

For example, power consumption may stop growing even while "real" consumption continues to grow. Or we may spread to other planets so that power consumption can keep growing and we don't care if the oceans boil.

Or something else might happen that is hard to predict in the same way that medieval people would find the Internet hard to predict. Medieval people may have made equally valid claims about bounds on the speed at which a messenger can transmit a message, even if you manage to develop a commercially viable racehorse that can run at top speed 24/7.

[Retric]

Medieval people where aware that you could send messages faster than a horse.

Flag signaling between boats is very old and eventually turned into a messaging system that could go 191 km in 5 minutes. Smoke signals where perhaps the oldest form of long distance communication, and was used across the full 7,300 kilometres Great Wall of China. Though actual speeds are less clear.

For physical messages, attaching them to projectiles or birds was also used. A man on foot or a horse had other advantages.