Yeah.. this is like the worst advise at this point. Rather than "doubling" your money, you will most probably end up losing all of your capital. What happened to XRP is just a trailer of things to come. In the coming months was can expect more and more altcoins to go down, similar to Ripple. The best thing to do is to hold on to your BTC, without diverting any of it for the purchase of shitcoins.
Yeah selling all your bitcoin for altcoin is really a bad decision and should be avoided. Either keep holding all your bitcoins as it is the safest investment and this is not the peak of bitcoin. Also note that if you still want to buy some altcoins then you can keep 50% of the money in bitcoin and invest the rest 50% in the good altcoins.