There is plenty of future potential for crypto currencies. However, there are a few yet to be addressed technical problems with the current blockchains that make them unsuitable for anything but speculative investment and very light/experimental usage (i.e. only a handful of transactions per meaningful timeunit).

The main technical challenges have to do with scaling issues. Facebook's recent proposal for Libra is interesting in the sense that it proposes some workable solutions for these. If you ignore the permissive vs. permission-less fundamentalism by some in this space as well as the political controversy, they actually did a fine job technically moving things forward with a better contract language than solidity and a loosely permissive and potentially long term permissionless system not unlike Ripple and Stellar.

Also, Ethereum is on a slow path to sharding and proof of stake. Sadly, that means it's currently unusuable for anything that requires scaling numbers of transactions/users. That in turn means most of what is currently running on it is a bad joke in terms of scalability. Most of the serious things associated with it happen on so-called side chains. This is just a fancy name for a convoluted and centralized database. Also it means anything building on the current version is going to face repeated disruptive forks in the network. That makes anything depending on Ethereum a proof of concept at best. That's the vast majority of (at this point mostly failed) ICOs on this platform.

IMHO a few things will happen in the next few years.

1) several of the currently well funded startups will start producing working products with actual users and revenue (the non speculative variety). Given the level of funding these companies received they would have a long runway for getting there and no rush to hit the market until several years from now earliest. In terms of tech startups, this would actually be relatively fast.

2) Most of the early startups in this space will fail. I expect a dotcom style consolidation phase where all of the BS, scams, etc. will fade away or be abandoned. This will take some time and be chaotic and generate a lot of negative news.

3) Several fin tech companies and banks are already integrating blockchains into their technology stack and the transaction volume depending on this will hit an exponential growth curve a few years from now. Most of this stuff is operating under the radar currently but are doing the right things from a technical point of view to make this scale. These will be mostly using permissive blockchains based on Ripple, Stellar, Libra, or similar.

4) Central banks outside the US and EU may start using blockchains because it makes sense. E.g. China has some plans here and and has an obvious opportunity to establish themselves as the digital currency of choice in most of South America, Asia, and Africa (basically anywhere with a weak, inflation challenged currency, and a lack of widely used banking products). Libra was after this opportunity as well.

5) Most of the utopian stuff in this space is IMHO doomed because it doesn't solve a problem people have other than fulfilling some political/idealistic agenda. That means I expect most of the financial success to be in permissive rather than permission-less systems. Legislators are pretty much going to require this for anything serious and most institutions with access to money are not going to want to come anywhere near the scams, criminals, and money launderers currently trading bitcoin. Bitcoin as such may survive as a convoluted alternative to owning gold (which is it's only use today).

6) The US and EU will take their sweet time adjusting their legislation. Short term we can expect nothing more than platitudes from ignorant politicians and very little in terms of any coherent/meaningful new laws in this space. The status quo is that most of the parliament members across nations lack the knowledge to have a coherent point of view. IMHO china is going lead by example here because they don't have this problem and have a clear incentive/goal. Then the west will catch up, eventually.