I assume they are saving that for when Fisk sets aside all pretext of being a legitimate businessman/politician and embraces openly his destiny as the Kingpin of crime.Both mentally and physically.
Which seemed to happen in the last scene with him in the last episode in the jail cell, staring at the white wall.…

History also says "slim" are usually made with cheaper parts and run hot..

You can use any laptop or with a cheap 3rd party mount desktop hard drive with the ps4..They really couldn't make it much easier to expand it..most people probably have a larger than 500 HD just lying around the house