First of all, it's a good thing that privacy finally arrives in "mass media" (is it okay to say that about TED?). It's also great, that more and more people are working on making privacy easy and available for end users. However, there are a number of aspects that prevent me from being a fan of the product per se (admittedly, I haven't studied the homepage of ProtonMail in too much detail, so please correct me, if I'm wrong):

To begin with, ProtonMail creates a closed ecosystem, which at the moment is only useable from within a web browser. Yes, there is an app in the making, but I'm speaking of standard protocols to use every mail client (which is also "requested"). Until then, it's really not usable for me.

Also, it requires both participants to be a member of the system as otherwise it's not working or would have to fall back to unencrypted mails. I assume that there must be a reason for them not just using GPG/PGP as backend.

Furthermore, the closed ecosystem also means that (to my best knowledge), you're unable to use your own domain and so on. At that point (only intra-system communication, no personal domains, ...) I would question, whether to call it "e-mail" anymore, at all. Which is NOT necessarily a bad thing. Just saying. It probably wouldn't be easy to "open" ProtonMail to the everyday mail traffic: Incoming mails wouldn't be encrypted (at least not end-to-end) and outgoing mails couldn't be encrypted to foreign domains rendering all the effort worthless.

The main problem, however, even if all the above things are "fixed" remains: There is still meta data. Which is enough to get you killed. While I truly admire the fact, that people are getting into encrypting mails, personally, I belive, that e-mail itself cannot be "secure" and should be replaced. By what, I do not know.

I realise that this quickly went from a "Things, that ProtonMail should (and probably will) fix" to "But there's no point in doing so, because e-mail sucks", which I do apologise for.