G'day. It looks like there is no way in-game to determine the remaining time of the ESO+ subscription. The buff doesn't have duration information, and the handful of API calls used in the store, etc, are just boolean: "am I ESO+, or no."
It would be great if there was a way to get the remaining time, so that it could be automatically displayed by addons; I'd like to have some idea when my next subscription tick will be, and thus when I'll see crowns come in. I'd rather that was automatically managed and in-game, so this request.