What statement is expected to be correct for a post-quantum cryptography world?

After quantum encryption and decryption technologies become mainstream, it is generally believed that nonquantum cryptosystems will be defeated with relative ease, meaning that quantum cryptography will be required to be secure. Qubits are quantum bits, not a measure of speed; quantum encryption will be the relevant solution in a post-quantum encryption world, and even very long RSA keys are expected to be vulnerable.