Not "auto trust", of course, but rather make adding keys is a bit smoother. As in "OK, there's this key on the web site with this weird short hex cookie. Enter this simple command to add the key. Make sure signature it spits out is the same on the web page. If it matches, hit Yes."
And maybe this could be baked somehow to the whole APT source adding process. "To add the source to APT, use apt-source-addinate https://deb.example.com/thingamabob.apt. Make sure the key displayed is 0x123456789ABC by Thingamabob Team with received key signature 0xCBA9876654321."