It is not clear how the new nucleotides act when transcribing proteins but assuming its at least as efficient as the 4 letter code it could be a very interesting option for artificial viruses. A virus engineered to be totally dependent on the new nucleotides could be used much more safely even inside humans where there is no supply of them, they could infect the cells, produce proteins and a huge immune response but not a single copy of their genetic material could be produced. Also in a controlled environment they would thrive (cheap production?) but without P-Z no danger of new virus production so safety would not need to be as strict.
Applications on real organisms probably will take much longer time, but the simplicity of virus would make it a natural first step.