"I'm still looking for a generic IoT product that isn't solving a problem that is already solved in older and arguably better ways"
And not just IoT products. This and the Moxie Marlinspike article listed above reminded me of an article which came to my attention a few days ago: https://trendoceans.com/a-simple-solution-to-the-private-key-loss-conundrum/
Basically it saves you having to remember your private key by going to an online random password generator which you seed from a piece of arbitrary text of your own choosing and a date. This gives, according to the article, 10 15 character passwords (I tried it and got 20 20 character passwords) from which you select 32 characters and from that generate a 256 bit key. The article provides a shell script for this. Repeat the process to regenerate the key as needed. It struck me that:
1. You now have to use a server whose operators may well be of the utmost probity - I'm sure they are - but who you have to take on trust as you don't know them.
2. You not only have to trust the current operators but any successors whom even the current operators may not know.
3. You have to trust the security of the server and everything linking you to it.
4. You have to hope that the server is still running for as long as you need the key.
5. You have to trust the reliability of the server, namely that it will give the same result each time. Note that the results it gave me a few minutes ago don't match the description in the article although it may be that the article accesses it via curl and I used a browser.
6. In place of not losing the key you've got to not lose the script the article describes or at least you've got to remember the URL and which characters the script picks out from the returned block of text.
7. You've got to remember your seed text and date.
I suppose you could keep all the bits you need to remember in your local Keepass database but then I suppose you could do the same for the private key you're in danger of forgetting.
And have I missed anything out from that list? (I've already thought of one extra.)