I see only one way around that, and it's prohibitively expensive: have the user assign aliases to public key signatures, and mark everything else with a big sca

I see only one way around that, and it's prohibitively expensive: have the user assign aliases to public key signatures, and mark everything else with a big scary "UNKNOWN". And I'm not even sure it would work: many users would just click the "yes I know them, please trust" button on first use. An alternative would have "unknown" be a little, not very scary warning (with easy TOFU), and the "this handle looks like this other one, they may be trying to scam you" blinking red warning. Then it would be on the developers to detect typos and look alikes.