Gut biome actually changes pretty rapidly. IIRC some grad student did some kind of sequencing on his stool for a year, the the populations of different strains of bacteria would completely flip when he ate a salad one day and a cheeseburger the next.

His name was Lawrence David, but I can't quickly find the writeup that illustrates the point I'm making.

Is this sarcasm?

I have accounts I haven't logged into for years, but still need access to. Losing access over time is not a good feature. And a 'reset' with antibiotics doesn't make sense for a bunch of reasons.

Also, password diversity is a good thing. I don't want $COMPANY_A's data breach to expose my password to $COMPANY_B

I like that if you eat a healthier and more varied diet you end up with a more complex password.

And you can share your password with the rest of your family with a fecal microbiota transplant.

It's going to be difficult to keep the sensor completely clean for the next person to use.

I already use it as my signature.

Why?

Or, we can develop solutions based on existing [proven] cryptographic primitives, with a focus of abstracting authentication / signing / encipherment functionality to an external key or secure-device.

Example: iPhone (and Andorid) both have "secure enclaves" where cryptographic keys are stored. However when you step into the basic PC/Linux realm the concept of a secure-device for key storage (TPM) is pretty non-existent outside of corporate players. We can do better, without totally going pie in the sky.