Quantum computing has already been made to work. If I remember it correctly, IBM successfully implemented Shor's algorithm and factored the number 15 using 7 qubits.

I believe that large scale quantum computing will happen if the technical challenges posed by decoherence etc. can be solved. Even if it costs hundreds of billions to build one, if it can be done it will be done because such a machine is able to crack the RSA code (using Shor's algorithm numbers can be factored in poynomial time).

Almost all of the secure communications can then be decoded using ordinary computers. You only need the quantum computer to find the key to decode messages.