I have thought about this before as its been brought up. The counter argument has been we have already done this for the last 20 years with IF coho. The interception rate on those fish has been less then 5% for a very long time and they have not recovered.
That being said 5 years is nothing, to a salmon that is essentially 1 generation. Really for this experiment to bare fruit it would probably have to be more like 20 years. Then a review of salmon stocks would have to take place. See what ones have recovered and what ones have not. Then based on all that data new escapement targets could be made.
I think we would see some stocks that would greatly benefit from this but others like sockeye we may not. Lots of sockeye stocks on this coast have not been fished for a number of years and simply have not recovered. Rivers inlet sockeye is an example of this.
https://www.theglobeandmail.com/technology/science/when-the-salmon-stop-running/article4160858/There is also a theory called Depensation or critical mass . Basically once a fish stock drops below a certain level it may never recover or may take 100's of years or some kind of natural event to get it back above that critical tipping point.
Then in the case of our hatchery fisheries well a lot of the returns are based on how much brood stock is taken and ocean survival especially on systems where there is little to no spawning habitat or the hatchery fish just swim right.
In brood terms tho I think we would see a good benefit but after those years we would still have to refrain from not harvesting them all.