Nice work! I spent about six months pursuing the exact same idea about five years ago with the hope of building a company around it. I got reasonably far with a prototype, but gave up on the business side of things after doing more extensive market research and interviews.

One of the people I talked to had been involved with a startup called Adrenaline Mobility which did something very similar, but ultimately ran out of runway and was acquired by Twitter. He told an interesting story about how they (over-)built a highly scalable service but had a really hard time selling it. Those who lack the training to know the difference between good security and hand waving didn't see the value, and those who did have the training and skills didn't trust a third party to do it right anyway.

Nonetheless, a lot has changed in the past five years, and end-to-end encryption is more widely appreciated now. I hope you have better luck with the commercial side of things; this looks like a very promising start.