Technically speaking, it was never exactly out of the realm of possibility for something like this to happen. I wouldn't call it the most astounding scientific discovery ever, but it definitely gives us more insight into the possibilities of alien life.
If this result proves to be correct, it will have huge implications for basic biochemistry. These GFAJ-1 bacteria in Mono Lake in California were able to consume arsenate in place of phosphate (an important building-block of organic molecules such as DNA) and incorporate arsenic into their chemistry. Even if this is an exception to the rule on Earth today, it implies that the biochemistry of extrasolar life (or even life on planets/moons in our own solar system!) may be much more diverse than we have previously assumed.
And why not? If there are zillions of planets and moons and rocks flying around in the universe, doesn't it seem sort of dumb to assume that life on them would only be composed of the same sorts of organic molecules we find here?
Assuming the universe is infinitely large.
And take the fact that we obviously exist.
The very fact that we exist relates to a 100% probability that other lifeforms exist, in fact infinitely many must exist in an infinitely large universe.
But then the rational nowadays is that the universe may not be infinitely big, but perhaps it is close enough, from our perspective, to infinity that the relation still holds.
Now on the other hand, there is a extreemly small chance that we will run into alien lifeforms in the vastness of the universe. The chance gets even smaller when trying to have two intelegent lifeforms meet each other in the same location in the vastness of time and location. Thats not to mention the probability of us being wiped out in the relatively near future.
But again with a near infinite universe, these meetings must have happened at some point, and it would be cool to think it looked like some mad sci-fi type shit.
So the probability of us finding alien lifeforms just got a little bigger, as now we can concider a few more astrol bodys as potential hosts for life, yay!
to be fair to NASA, yes, it was always possible life could exist on.. well..
an arsenic-based planet/moon or something.
but with their limited budget, and the previous consensus that life in arsenic would be impossible, wouldn't it be worth their time and money to NOT explore such things?