Maybe in US this holds, but things may be different in different places. I'm a Chinese living in the bay area. I think people here treat E-mails as part of their daily life probably because most of them began to use it before the mobile internet is a thing. On the contrary, in China where the majority internet users are mobile-savvy, WeChat is the new email. Actually E-mails are only for official communications there…
Email is a standard. There are multiple providers. It's a great lowest-common-denominator.
Does any company really want a part of that without changing the above? I thought Uber establishing a "defacto standard" for ride-sharing which can be copied by competitors is one of the strategy points we criticize here on HN?
I don't know the Chinese market, but just keep in mind at some point everyone thought that FB/Twitter were going to kill RSS. Fact is, RSS is still around and being used a lot (Podcasts?). While FB/Twitter have restricted access to monetize (or prevent others monetizing) their proprietary platform.
Email will be still around when WeChat is dead and gone.