One front-end for multiple servers is how you end up reimplementing XMPP (bar federation) before you know it: servers are not guaranteed to run identical/compatible versions -> you bake versioning at capability level in the protocol -> you make clients and servers degrade predictably when that happens -> you write a standard to document it formally -> you invite around the table those authors of alternative client and server implementers and boom, you've got the X in XMPP, and the XEP standardisation process and the XSF to support it.
I bet this does a kind of "iframe" thing, where you're really just pulling in full web UIs, and they can be whatever they want. That's the impression I get from the comment about phone clients wrapping the web UI because there's no guarantee about what they will actually be.
