You could argue that, with 4K TVs a relative luxury for gamers at the moment, it's not a desperately needed feature, especially if it keeps the overall cost down. But it will age the console, preventing it from being fully future-proofed. What's perhaps more annoying is the complete removal of the optical out audio socket, which could cause headaches for those with older AV equipment.
However, one upgrade that is coming to the entire range of PS4s along with the PS4 Slim is HDR support. It adds greater detail to light sources in an image, and is considered the next big thing in TV tech. The roll out is still in the pipeline, so we've not been able to test it yet. But rest assured that the PS4 Slim will support high dynamic range shortly.
All other streaming services and apps featured on the PS4 return for the PS4 Slim. They include(but are not limited to) Netflix, Amazon Prime Video, as well as BBC iPlayer and TV from Sky in the UK, and HBO Go and Hulu in the US. Sony's own movie rental platform is available too if you're looking for the latest Hollywood releases. YouTube is available, as is Twitch game streaming, and a Spotify Connect-enabled version of the popular music streaming service, letting you control tunes on your telly from the comfort of your smartphone.
