I'm not convinced we'll actually see Scorpio in 2017, tbh.
If you want to play Fifa 17 - or you want to play Fifa 18 when it comes out - the Slim is your best bet. I mean, if you were planning on buying the game anyway, for about £40, you're getting the console for £159 there, which ain't bad at all.
If you're only interested in Fifa 19, and couldn't give a flying fig about 17 & 18, and you have a 4k TV, and you have about £400 spare then you're right - better to wait for Scorpio (or whatever they actually decide to call it) to come out.