Despite being a very early test mule, this test car features a wider track and longer wheelbase than those of the current Focus, suggesting the 2018 model will be a larger car overall.
Evidence for the modifications can be found with a seam that runs down either side of the car and from the front to rear. It suggests additional material has been added to the body to disguise the stretched underpinnings.
Inside, we can see what looks like a simplified version of the current Focus's interior, although this modification is likely only related to the test car.
The current third-generation Focus was released last year, so its successor isn’t due until 2018. Given how far off this is, it's unsurprising that Ford wasn't able to offer any more information at this point.