Got this working on my old Galaxy S3. I am thinking about doing it on my Galaxy S5 now. Sounds like people over on XDA, myself included, are having issues with janky connections via WiFi. It appears to be something with the app for now. I can use Remote Play with my Vita all over the house, without issues. If I do it with the S3, over my Wifi (just like the Vita) it never wants to connect.
However, it connects just fine if I am in the same room as my PS4 because it is using the direct connection. This is just a "hello world" proof of concept for me because if I am going to use Remote PLay at home, I am going to use my Vita. However, I am tempted to try it on my Galaxy S5 over my 4gLTE connection to see if there is any difference.
When I installed this at first, I was getting the 800Error or whatever and remote play didn't want to launch. But thanks to some tips on XDA, I uninstalled SuperSU and everything worked fine after that.