As far as I know, and I could be wrong, ProtonMail wraps around pgp inbox encryption. Many providers have exactly this service already.
The difference seems to be that ProtonMail don’t allow you to use normal imap and your own client with pgp, but force you to use their client. This is probably a trade-off made to protect users against them selves in one way (disabling encryption for grandpa) and hiding the non tech-savvy from all the technical details.
Again, many assumptions here.
So, to me, mentioning proton here doesn’t make sense as the underlying tech: smtp & pgp have existed and been industry standard for a long time. So there is not issue of adoption.
The difference seems to be that ProtonMail don’t allow you to use normal imap and your own client with pgp, but force you to use their client. This is probably a trade-off made to protect users against them selves in one way (disabling encryption for grandpa) and hiding the non tech-savvy from all the technical details.
Again, many assumptions here.
So, to me, mentioning proton here doesn’t make sense as the underlying tech: smtp & pgp have existed and been industry standard for a long time. So there is not issue of adoption.