First option not on the list: revoking self-signed SSL certificates. Normally, it's hard to revoke a self-signed cert, because a potential attacker can just fail to send the user the revocation. But put the revocation on the blockchain, and timestamp the original cert, and it all gets a lot better.
Second: Time-release encryption. You can build a public key such that the private key can be computed from any future set of blockchain hashes. PDF paper. That makes it actually time-release, instead of a lot of schemes that release in response to a certain amount of work being done.
By a quirk of history, this particular culture won and imposed it customs on everyone else.
There's a societal down-side to polygamy, one that needs STRONG cultural overrides to prevent. If (presumably) richer men are allowed multiple wives, that means that there are fewer wives for the rest of the men. You then end up with an excess of unmarried, non-parental young adult men, and being married and a parent is usually a calming influence. These single men are usually the first in the streets if things take even a tiny down-turn. We still see this in Arabic countries which allow polygamy, as well as countries where there's an imbalance of men and women, such as China and India (one-child policies as well as gender-based abortions responsible.
This is an obvious problem in societies that also have the problem of being strongly patriarchal and/or misogynistic. (The obvious examples you site have these issues.) In cases where women are equally allowed and able to engage in such relationships, there is no a priori reason to suspect such a problem.
The only evidence I know of that is directly relevant to modern times and from a sexually equal setting is highly anecdotal. I've looked a little for better without luck. But, what I've seen and heard from the polyamory community is that this is most likely a non-issue, and that if it isn't, you probably have your genders reversed. Basically, I've seen weak anecdotal evidence that in some circles, the women tend to participate in more relationships than the men do. I haven't seen any evidence (weak or otherwise) of the reverse effect. And, of course, this report should be taken with a large grain of salt, as it's based on fairly strongly selection-biased sources. However, I think it's strong enough to call your fears into question.
For reference, I (male, straight) in a happily polyamorous relationship. My partner (female) has a paramour (also male, also straight). The three of us get along well, and none of us are actively dating anyone else.
You can distill helium out of the air. There's some left. The cost would be around 10x the cost of neon, though. And if you have to ask what neon costs...
Actually, people do distill some helium out of the air. It comes out with the neon as "noncondensing gases" in the column. Those gases get sold to some buyers of neon, who don't mind some extra helium in the gas. Neon signs aren't too picky, iirc.
There have been cases of criminals finding ways to substitute another person's DNA for their own, including one case of a doctor who actually managed to hide another person's blood in one of his veins, thus faking his innocence.
Do you have a link for that? It sounds fascinating.