At risk of repeating myself: determining whether damage has passed information-theoretic death falls under the purview of physics and cryobiology, among a variety of other fields. That is not at all the same thing as saying that it is "in the area of expertise" of every physicist and cryobiologist, and thus a (hypothetical) survey of them would be "expert opinion".
I agree with what you are saying here and think you've struck the right balance between acknowledging genuine competence and expecting universal expertise over general fields of knowledge. Elsewhere and at a different time it might be worth having a conversation about how to select experts in subjects similar to this one. There is something of a recursive problem in as much as it requires knowledge to know which experts are the ones that are relevant or knowledge to know which person to ask-which-people-should-be-asked. Different beliefs about how to choose authorities to believe seems to be a huge source of disagreement over a variety of problems and frequently results in "reference class tennis".
In the past, the Cryonics Institute has had a policy that said that they would not accept anyone who is not a member. This has changed. The policy now is that someone who has full legal authority over your body can sign you up after you die. It costs $36,250 to be frozen if you are not signed up, which is more expensive. They also will not do anything until you have been on dry ice for 2 weeks after they have been contacted, so not being a member is more risky.
This is very important news for anyone who is currently cryocrastinating. It means that you can drastically increase your chances of survival without filling out any forms. All you have to do is tell a loved one you want to be frozen upon death, and that you would like them to take responsibility for making sure this happens. This takes literally 30 seconds. Do it now!
This news might also be a reason to not sign up right away, if you think something better (like radical life extension or uploading) will come along in your lifetime. We should discuss this in the comments.
Edit: The general consensus of this discussion is that this is a really bad reason not to sign up for cryonics.