I am in the process of putting together a liquid chlorine feeder for my pool and I wanted to get clear about something...

When I add a gallon of 6% bleach to my water, it will raise the FC by 2.1 and the salt by 3.4. Now this is something I could be doing sometimes on a daily basis. So my question is: though the FC essentially completely leaves the water, the salt remains to accumulate. Is this not a much slower version of the CYA situation? The salt will build up over time without draining ?

So if you can taste 2000 ppm of salt, you will notice this buildup after about 600 gallons of bleach? (minus whatever salt is in the water to start with?)
Seems like a 4-5 year cycle..??

Is this right?

Most forms of chlorine will either add salt or calcium.

Most people have to drain/refill due to high calcium long before salt is a concern.

Most people like the effects of salt levels around 2000 ppm. Taste is subjective but the salt will incease so slowly you will likely not even notice it.

You are basically correct that it takes years for the salt level to build up, assuming no water dilution, and that at some point a partial drain/refill would be needed. This is far longer than would occur with a CH rise from Cal-Hypo (or from evaporation and refill of high CH water) or from a CYA rise from Trichlor or Dichlor. Also, with backwashing/cleaning of the filter and water overflow from summer or winter rains, one usually has dilution of the pool water on a regular basis. In my own pool, I use winter rains to dilute the salt increase from chlorine and Muriatic Acid by roughly 50% each year so I keep the salt level in check at under 1000 ppm.