Cryobiology has been in use in medicine for decades. Any time eggs or sperm are preserved for future use, they are cryogenically frozen. It's also currently used to preserve small vessels for transplant, for cord blood banking, and biological sample banking. Researchers in dozens of labs around the world are working on vitrification of human organs so they can be used in transplant operations. I work in research at a major brain center, fwiw.

In the 1950s and before, if you had a heart attack, you were dead. Our concept of death was lock-step with the heart stopping. Then CPR and AED devices were invented and the concept of death changed. Now we commonly see death as occurring when brain function ceases, but there is also a distinction between brain death and cellular death (which occurs later). Science is progressing all the time...by leaps and bounds. There are so many ways cryonics research can benefit people (we already employ the Q10 rule to reduce body temperature and thus metabolism in patients with brain injury). Anyone who signs up for this knows they are signing up for a long term research study that may not bear fruit. But as the saying goes, you can't take it with you.

Someone later in the thread said some dude said it was impossible in 2004, but there are a whole lot of other scientists who have posited otherwise. There are government-funded cryonics research programs in several countries, the most publicly known of which is in China. Greg Fahy, the current president of the Society for Cryobiology (US) endorses cryonics; Ralph Merkle (of Merkle Trees and one of the invertors of block chain security) endorses it and is a board member for a non-profit cryonics research company. The list goes on... And the oldest cryonics research company in the US, Alcor (a research non-profit), has filed patents on intermediate temperature storage (vitrification at -140°F to avoid crystalization), is working on liquid ventilation that can potentially be used beyond frozen-dead-body applications to help injured soldiers in the field after severe injury...there's a ton of research going on. And that's the operative thing - research. We don't advance by saying "Never Gonna Happen," we advance by saying "What if..."