> For people who own Bitcoin at this point one of the only thing kinda sensible to do is to use multisig schemes, like 2-of-2 or 3-of-3 multisig, where your split the secret over two or three different hardware wallet brands

What about ignoring proprietary hardware wallets, and implement your 'wallet' as a small, bare-bones, self installed debian system with enough empty disk space to be a full node, that stores the data on a dm-crypt volume? Buy the hardware in cash from a random used computer store. No it won't be as convenient and portable. But if you trust standards-based crypto, you can implement your own ssh tunnel or whatever to it from your other client devices. This also lets you take 1:1 disk clone images of the dm-crypt volume and safely back it up to remote locations at any time you want.