I had same question but it was answered by dev. Coins that are used to buy FeeShares are redistributed by dev to users, via the multipool and the 60% pos from exchange.
Yes, that trumps the initial math and allows for, eventually, all the feeshares to be sold, all right ... but, so far, no redistribution has taken place to miners and no PoS in Exchange either

That's half correct. The first distribution from the multipool took place a few days ago and a buy order was placed on the exchange for the equivalent amount of Bitcoin.