This long and detailed analysis (by Rakesh Upadhyay) of some of the prominent crypto coins starts out with a claim that a 40 trillion market cap can be reached in 10 years.
https://dollardestruction.com/2018/04/29/bitcoin-ethereum-bitcoin-cash-ripple-stellar-litecoin-cardano-iota-eos-price-analysis/
Compared to many estimates, I think this one isn't far outside the realm of possibility. It essentially means that it becomes as large a market as the current global markets in traditional equities, assuming those markets continue to grow, then crypto matching that market size isn't an unreasonable expectation. But a lot of things have to happen. The business world at large needs to see the value of crypto. That 40 trillion represents a huge influx of capital from fiat into crypto. The only way for this to happen without destabilizing the global economy is if there is enough economic growth to absorb that increase. Look at it this way. If people simply pull money out of stocks and bonds and stick it in crypto, then it's a wash, economically speaking. The value has simply been moved from one place to another. This is why crypto must show real value and why in the end the faster we get rid of shit coins and support projects with a real value add to the economy, the sooner we can get to that 40 trillion.