The PS4 Slim supports the faster 5GHz wi-fi, which is an upgrade on the current PS4, which only supports 2.5Ghz.
Twitter user @shortmaneighty2 showed off a picture of the manual, which reveals that 5Ghz is indeed supported, although there's no indication if there are other differences between the consoles at this time.
PS4 Slim has yet to be announced by Sony, despite some people owning it already. It's possible that the console may support 4K Streaming and who knows, it may also include a 4K Blu-Ray drive, although at the moment it seems like the latter is most certainly reserved for the PS4K (Neo) console.
Sony is expected to announce both the PS4 Slim and the PS4K at an even next month. We're not sure what else will be announced, but it'll be exciting finding out.