It will be interesting to see whether this gains any traction once it hits the exchanges. I'm linking to a very interesting article which suggests that a cryptocurrency index fund actually underperforms Bitcoin over the long term, because even though alts go up more in bull markets, they go down more in bear markets while Bitcoin holds its value.
http://woobull.com/crypto-currency-index-funds-the-simulations-have-surprising-results/
This if from a year ago, when there figuratively were no alts, nor any ICOs.
That's true, but Bitcoin still hasn't even begun to go up. In fact it's only at fair market value relative to it's long term trend. You watch it go up 3x overnight just like Monero did, or even more. Then it'll be interesting to watch all the alts and the ICOs on the way down...
What you are neglecting to consider is how the relative value propositions of different altcoins are going to change - many altcoins are vast improvements over Bitcoin and offer much greater utility - Bitcoin simply has the majority of investor confidence and public exposure but this will slowly change. Bitcoin will not reign forever.
Altcoins were in their infancy when this study was done and as such the results are no longer particularly relevant - as the market matures to resemble an ecosystem more like the real-world stock market index funds will become increasingly relevant.