Never. It's simple plain economics. It might have been able to do so if it was made on POS from scratch or in early 2010 but as of now when BTC price is 60k there is no chance one can even think of switching to POS. Just imagine the investment that would be required to buy your stake and keep it in and despite that, the new miners will never be able to hit their profitability mark anyway because the early adopters will always be having the edge. This would ideally make mining unprofitable for anyone who has started recently. Also, if you look at it from another angle. Also if the pools vanish altogether for some time. Chances are that even a 51% attack can be made on bitcoin. Satoshi created bitcoin so that even on his own cannot manipulate it after creating it. But in POS let's say if he decides to stake all his coins for Mining he can literally control the mining altogether.