If you want to download the client to use PS4 Remote Play on PC or Mac now you can, as Sony Computer Entertainment made the download page available.

You can access it here. The client is rather lightweight on PC (16.8 megabytes), and the system requirements are the following:

PCMac

It's worth mentioning that the PS4's system software update 3.50 is also required, so this won't work until you download that as well.