I don't know what their endgame would be, if it was a body double

There's no long term benefit (read: more than a few days) to having a body double. Given how much press the POTUS has, it would never work as a long term ploy.

The only "maybe" possibility is that they want to delay the news of his (potential) absence for a few days. Which i don't know why they would, and i doubt this would be their strategy

So, IMO, it is him, and he had a health scare or something similar