"Such a solution would basically be as secure as their servers."
And who would secure the servers?
The team that secured Talk Talk, Ashley Madison, JP Morgan Chase, Linkedin, Sony, Walmart, Yahoo, Verizon, US Department of Defence, UK Ministry of Defence?
All the above have been hacked: https://en.wikipedia.org/wiki/List_of_data_breaches
As soon as a backdoor or MITM access is given to end to end encryption it becomes insecure. And anyone concerned with security using it would switch to another method.