I think ubiquitous end-to-end encryption is the inevitable future of 1:1 and group communication. The momentum is in that direction. In your case, supporting the browser as a platform rules it out right now, but hopefully that will change when browsers provide an environment for doing serious crypto, where the server can't just quietly push down some new JS that leaks messages back to itself.

I'm in the alpha stage of building an end-to-end encrypted social network (https://sharewithsup.com, invite code: eff, currently iPhone only). Under the hood, it establishes E2E group channels between friends and uses those for everything (posts, comments, photos, events, etc). History is relayed between friends and search uses a local index, but the UX is still similar to Facebook. My point is - in addition to namedropping my app - that it's possible to find ways to implement features that at first seem hard with E2E. Just not on the web, yet.