Same question. I have one friend, smart and technical but just middle-of-the-pack when it comes to his non-domain-specific computer skills, and I got him using PGP regularly in our communications. He insisted on using webmail so we went with Mailvelope which mostly worked well up until it seemed to be losing his keypairs. He got pretty frustrated with that so now we're trying the ProtonMail approach and hoping for the best. To your point though, we've exchanged many dozens, perhaps 100 PGP-encrypted emails over the past year and I'm sure he's never heard of a "key-signing party".