This ice was central to the theme of the Mars trilogy by Kim Stanley Robinson: Red Mars, Green Mars, Blue Mars. Earthling colonizers were able to terraform Mars as easily as they did because of the huge amounts of water ice under the surface.
Robinson theorized this vast amount of subsurface ice for his novels, partly because it greatly helped his process of terraforming, but also because he felt he had enough scientific basis for it being likely. Now he must have a big grin on his face at this news, feeling vindicated.
Like I said, the idea was already out there. It had a sound scientific basis, which was why he felt he could rely on it in a hard science novel. He must now be feeling quite relieved that it turned out to be real, after all.
I had the same thought when I heard the news. Sure, it was theoretically possible that there was some subterranean (submartian?) water present, but KSR theorized that it was abundant, and popularized the idea. And now it looks like even his estimate may have been conservative.
On the other hand, most of the conflict in the Mars trilogy was based on the assumption that overpopulation of Earth would continue to increase into the 22nd century, by which time there would be over 18 billion people.
That’s almost certainly not going to happen, so the trilogy is still off on some major details.