Nothing prevents it.  And I hope we see greater use of the blockchain as a global trustless ledger moving forward (e.g., colored coins, oracle-based sidechains, etc.). 

But it's important to remember that the only asset that can exist on that ledger free from counter-party risk are bitcoins.  In times of crisis in this blockchain-based future you're imagining, market participants will tend to trade out of assets with counterparty risk, as well as out of oracle-based sidechains, in favor of the one asset that is itself its own backing: bitcoin.  I image bitcoin then as an attractor within a complex dynamical system; there's a constant flow of capital in and out of various blockchain assets, but these just circle around bitcoin.  Bitcoin naturally becomes the reference point¹ from which to measure the value of everything else.   In other words, bitcoin becomes money.

¹And the value of bitcoin is tethered to the cost of real resources due to the great physical efforts (mining) required to produce them.