To use js-ipfs, you still need to host the script somewhere. Doesn't help when the whole host doesn't respond.
js-ipfs, the Javascript implementation of IPFS, has made a lot of progress in the past 6 months. It's still early but totally usable.
We've been working on go-ipfs and js-ipfs interop so that browser nodes can talk to "native" nodes. It's not fully ready yet but soon. This will open a lot of doors for a more advanced network and applications using IPFS.
See https://github.com/ipfs/js-ipfs.
As for your question re. ipfs.io using js-ipfs, the answers is no, it doesn't use js-ipfs implementation yet.
I'm particularly interested in using ipfs pubsub capabilities. It looks like an interesting way of allowing multiple users of a web app to talk to each other without needing (much) server side support.
There's an old version (from June) of Orbit at http://orbit.libp2p.io which you can try. Much has happened since and we're working on bringing the js-ipfs version Orbit back to a working state.
Re.Pubsub, I'm personally also very excited about it! :) The specs and general info are located here https://github.com/libp2p/pubsub. go-ipfs merged pubsub into master some time ago with this commit https://github.com/ipfs/go-ipfs/commit/e1c40dfa347e38bdc9812... and we're working to get it into js-ipfs here https://github.com/ipfs/js-ipfs/issues/530.
IPFS and Matrix seem to be the only teams doing this: Dat and SSB have vague protocol documentation at best, only documenting bits of the protocol at all.