Remember, if you are an alt-coin investor and you want out, you can't sell for cash. There's only one way to go. It's to swap your alt-coins for bitcoin.
This is very true, this will probably end up happening, but I think I'll leave my money in the Altcoins, I'm doing hold during this year, and I think other cryptocurrencies have more opportunity to provide better profits.
Another issue, is that in my country is already negotiating for example 3 or 4 cryptocurrencies directly with fiat, and there are more and more similar alternatives, so in the future, I think we can change many more cryptocurrencies directly with fiat without mediating with the BTC .