I think and this is just based on my own research into the giants as dh is a huge fan and we will always have a Saint or Newf in our house with whatever mixed shepherd/collie thing I drag home from a rescue, that the life spans will begin to increase. The dogs being bred 10-12 years ago are much different than those being bred today. At one time size meant everything and the giants were almost ruined by it. The jokes it took them 45 minutes to circle the conformation ring, or they were winded and done half-way down, they were jokes, but a frightening reality. With well-bred dogs and breeders, breeders breeding to better the breed, to reestablish the breeds to their former glory and aptitude which was working dogs, rescue dogs, the sizes need to diminish. Many of the original Saints were lost doing rescue work, the foundation of the breed, as a result they were out-crossed to Newfs, which, while very similar have a different body, you will also find people looking to make the dogs bigger breeding to mastiffs.
We are fortunate with our Dolly, she has some issues which are rescue dog issues, she's clingy, she is tight-lipped, but we still have to wash the walls almost weekly, she gets water outside and has a heated water bowl because she will wash the floor and I don't care how much you think a GSD sheds, it is nothing to a Saint, think thick double coated GSD X 3.
I do believe though, because we do realize we are lucky with her, the next dog we will be going to a breeder who breeds for temperment, not size, who does health checks etc. I wouldn't rule out a giant or larger sized based on health, because the times are a changing, the public and breeders are becoming more educated. I mean we get the "OMG you should get her up to 200lbs" - OMG how bout we don't! She's far better at her height and weight and healthy, or she seems small for a Saint. She's top end of the height for a bitch, she also grew a bit after we got her.
The reason I say it, there are so many large and giants in rescue, they are hard to place, not everyone can deal with them. Imagine a 150lb, hairy, drooling lap dog - like the worst date you had in college everyday in your home for the rest of your life.
I believe you will see longer lifespans in these dogs.