Currently BTC prices have been hovering at 6000, and if the BTC prices fell to $5000, $4000 should be not far off, the market is confirmed in the bear market, want to rise to $20000, you may need a couple of years. 
Well theres nothing impossible. Maybe that would be happen but I think it needs patient so that you can wait with a vibe. $20,000 is a big amount but hopefully bitcoin could raise hugher than that.