My idea isn't completely automated but I am in the process of building it to help with water changes because I rarely do them with the hassle of buckets and mixing salt and such.
I am plumbing a garbage bin between my overflow and my sump. During everyday operation valves 3 and 4 are closed, R/O is closed heater and pump are off. Water will flow in and out of the garbage can and it ads more water volume to my system.
When I want to do a water change I open 3, close 1 and 2 and the container is now cut off from the system water. I drain the container with valve 4 and once empty open up the R/O line, it will fill with the float valve, I dump in the salt and turn on pump and heater. I will have it plumped into my R/O unit and my house waste line so I don't have to handle the water or pipes at all. Once the salt mix is to my satisfaction I open up 1 and 2 and close 3. The container is now back in the loop and I had just completed about a 30% water change.
An added bonus I think is I can gradually open the valves to introduce the new water slowly back into the loop.
I know this is no 100% automated process but its going to make my water changes a lot easier and free up my time to stare at tank inhabitants more lol.
I haven't figured out the overflow for the container yet, I dont want to hear a SSHHHLLLLUUSHHHHHHHH from inside the container haha.