To get the return they will have to buy in or already hold the ETH. There's only going to be +-100 million Ether w/ small inflation less than 2% per year. A common misconception is that ETH has unlimited supply mostly made up of Bitcoin Max. trying to knock the price down. Ether actually has a very finite supply. Ethereum Foundation just does not want to release official number yet until they get first hybrid Casper release most likely around late winter with the next upgrade. The return is going to vary upon market demand, how many nodes stake and amount of gas being burned. Looks like full release will come out in 2018 which would only leave about 5-7 million more ETH to be mined, then once POS released supply is basically capped. So even lower inflation than Bitcoin will have. I think once finally details come out it will be very positive for Ethereum's price..