One interesting thing that probably no one has talked about because it would be an atypical application of an esoteric economic concept is whether there is a strong "elasticity of substitution" between different cryptocurrencies. Normally, this concept is applied to inputs for production, but I think it's reasonable to consider in the form of inputs into a portfolio. You want to generate the highest return for your portfolio so the optimization scenario is similar.
Now that Bitcoin isn't even the biggest network in terms of on-chain transactions, how do potential buyers or users of cryptocurrencies choose what coin to use or invest in? With the idea of elasticity of substitution a buyer/user of crypto will consider the marginal returns of a coin purchase at a given price for a specific duration. So if you're comparing Bitcoin versus Ethereum, the marginal return for Ethereum might be expected to be higher given that Ethereum is newer, bigger, growing faster, generating more users through ICOs, etc. etc. So this would be in real numbers like saying (as an example): Bitcoin has an expected marginal return of 2%/mo. over the next 6 months but Ethereum has an expected marginal return of 4%/mo. over the next 6 months. Given this perception Bitcoin will lose overall crypto market share to Ethereum. And this appears to be what has happened over the last year or so as Bitcoin has lost market share to other coins.
Around the same time Bitcoin started to increase by huge percentages Ethereum, the second largest coin, was increasing at an even faster rate. This would strongly suggest that the market preferences were fairly elastic in substituting Ethereum for Bitcoin given the relative expectations for growth between the two.
It seems with the recent boom and bust with XRP that this elasticity of substitution was again in effect as traders flocked to XRP with expectations of higher marginal returns than BTC or ETH.
Given a longer duration timeframe for investment and evaluation of cryptocurrencies I think you will see this effect continuously as a distribution of risk preferences will show a strong substitution effect between larger coins and less developed coins (XLM, ADA, and NEO being other good examples) due to expectations of relative growth.
However, perhaps because the overall crypto market is so small and almost nothing of "real" economic value has yet to be created, the ultimate substitution effect could be with fiat currency or a less volatile asset class depending on various macro considerations.
Given this basic concept I can see Bitcoin stabilizing in value over time as it matures with better policed institutions and less volatility. However, this will likely take a long time and a lot of things can go wrong in between. And given quantum computing and other new technologies it's highly probable another system will emerge that will prove to be superior to Bitcoin.
This generally deflates the idea that Bitcoin will be $1 M a coin some day. Given the strong elasticity of substitution and the ease in creating competing coins/networks I think the overall crypto market would have to grow to a level that doesn't seem realistic given problematic utilty and centralization concerns.