This has been in place on other channels for some years in the UK (and other countries, though Sky is definitely a market leader in actual widespread implementation).

It is worth noting that the US and UK aren't really equivalent here, as the UK broadly broadcasts the same channels nationwide all day with already existing slight differences for geographically relevant advertising, not just during primetime. In some cases this is handled on a satellite platform like Sky by broadcasting 20+ regional variations of a channel, and that is literally nuts. A solution like this saves an awful lot of bandwidth.