Does anyone know if you will be able to replace the hard drive with a SSD?

Highly likely. I mean it is just a SATA device. The PS will not even know the difference. I also plan on doing this at some point.

I really hope PS4 will support it properly. The PS3 could utilize one but it had no impact on load times or anything from what I read, which was a bummer.

Most definitely. Whether or not it will have any tangible improvements in loading is the real question.

No reason why not, as to if the software is able to make use of the read/write speed well that's another question.

That is my main question I guess. I know you could in the PS3 but it was virtually useless since it was no faster than a standard HDD.

No real reason why it shouldn't work, they have to be building the hardware in a way that would take full advantage of an SSD.

Only problem is the price. A 512gb SSD costs about the same as the console itself. Not sure how practical that is. They better also offer usb 3.0 external hdd compatibility like the xbox one. Obviously not as fast, but you can get 1-4TB drives for a fraction of the cost of an SSD and you don't have to sacrifice the internal drive.

I hope you can, otherwise my horses will be so slow!

@noremnants:

Seems like some improvements can be seen but nothing to brag about. Seems like games are likely to load up slightly faster and installing should be faster then that but is it worth the upgrade? Also seems like it might fix some of Rage's texture problems.

http://www.eurogamer.net/articles/digitalfoundry-can-ssd-upgrades-boost-ps3-performance

I've noticed loading times for Last Of Us are really short with an SSD. I did bought the digital version so no reading from the disc. I can imagine it has the same sort of impact on the PS4. It'll be a bit more smoother and faster overall, but the biggest win for me is no HDD read/write noise but pure silence. The original 80GB HDD in my PS3 was very loud.