gx is a generic package manager on top of IPFS that uses git-style hooks for adding per-language support. It's already being used to manage dependencies on the go-ipfs project: https://github.com/whyrusleeping/gx

Bonus: there's also a IPFS git remote implementation! https://github.com/cryptix/git-remote-ipfs

Yes the IPFS implementation might change but not the content multihash addressing. Linking to data with those addresses is the generic 'package management' that solves all these problems (references to mutable data at mutable origins, circular dependencies, data caching, namespace conflicts). The specifics of resolving links will hopefully be something we don't think about much.

I've played around with ipfs.js for resolving links into eval'd js at runtime and imagine a npm replacement would be pretty trivial. The IPFS peer to peer swarm seems stable to me but you could also dump all your hash-named files into a s3 bucket or something as a fallback repo.