I just wanted to report that swapping out hard drives on the PS4 is about the easiest thing in the world. It took about 5 minutes to take the case off, take out the old HD, and put the new one back in. It doesn't take long to reinstall the OS either. You'll have to reinstall games and download updates, but you can do that during down times.
If you need HD space and you have the money to sink into a bigger HD, it's worth doing. Just make sure the one you want to buy will fit in the PS4 - and that's pretty easy to find.