Can you put your PS4 hard-drive into your PS4 Slim without issue?
Solution 1:
Based on this comment and answers on the PlayStation blog you CANNOT just swap the drives over. - The Hard drives are encrypted and keyed to the system they are in.
You can however back everything up to an external drive and then copy this data to the new system once you have it. full instruction on how to do this can be found in the PS4 user guide