I definitely think going with an X this late in the gen doesn't make a huge amount of sense if spending on gaming is a concern. As you said, the Scarlett is out next year.
As for going with the One SAD, I think the best way to go about this is asking yourself which games you're interested in on the Xbox One. If you can name enough to justify the purchase for yourself, go for it (keeping in mind the cost of the games as well, unless you go GamePass)! If there isn't enough compelling stuff you want to play, best to just wait for next gen. The Switch and PS4 have great support still so you should have no shortage of great stuff to play no matter where you game.