[higherpurpose]

If Google doesn't provide a serious End to End encryption solution for Gmail, then I will probably use it, too, within a year (unless something better comes along, say like a DarkMail-enabled service).

BUT, and it's a big but, I'd only use it for normal e-mails, just because I want to raise a big enough obstacle for NSA to read even my normal e-mails. However, I would not use it for anything too sensitive. I don't trust ProtonMail for that, and since it doesn't have real end to end encryption, you have to trust ProtonMail.