Citigroup has just released a research report making a bull case for cryptocurrencies — an asset class that hasn’t had a lot to cheer about the last two years.

The thesis is that blockchain and related technologies will grow to having a billion users and trillions of dollars in value over the next six to eight years. What’s missing is the implications for investors, which I’ll try to outline.

The 162-page report starts with the example of someone in 1900 predicting the eventual massive economic and cultural change caused by the automobile. It was not practical to invest directly. Most automobile start-ups at the time failed. Ford was not founded until 1903 and didn’t go public until 1956. Shorting buggy-whip companies sounds clever but it wasn’t any more practical than investing in car companies. Plus, buggy-whip companies had little trouble shifting to making similar consumer goods.