In my opinion, 3-4 altcoins (together with BTC) will remain being popular in the near future. (I strongly believe that Libra will be one of them). I hope there won't be thousands of altcoins people invested as now.
Well, I doubt there will be less than 5000 altcoins in the future considering the developing technology and the interest of humanity to the developing technology for making things easier for everyone. The unemployment rate will decrease if the tech people shift their jobs to the new crypto projects that have great future potential. BTC will not disappear no matter how many altcoins gonna replace their standings on the coinmarketcap.