Looks like they evolved DNA polymerases that are able to incorporate RNA or DNA bases when copying a DNA or RNA template. This is the first time a DNA polymerase has been known to have this capability. But, of course, there are already transcriptases that copy DNA to RNA and reverse transcriptases that go the other way around.

Natural enzymes tend to evolve for specialized roles. In nature, there are going to be RNA and DNA bases around all the time, and you don't want to randomly incorporate them in mixtures.

I guess the advantage here is that these have higher fidelity, so they could be very useful for molecular biologists who want accurate RNAs or RT reactions.