A lightweight markup language (e.g. Pandoc) + git (Score 1)

Depending on the complexity of your layout, I'd recommend, not LaTeX itself for the main collaboration, but one of the lightweight markup languages which is at least capable of footnotes, and possibly has a usable mechanism for citations.

This way you have a relatively simple, plain-text markup to learn, which can easily be thrown into git or another vc system. (Try a paid github account, for example).

Pandoc (using citeproc) was mentioned above. It's basically just Markdown with some refinements. The Citeproc part is new, but shows promise as a modern BibTeX replacement, and could be used with Zotero (which itself will get collaboration features, but not until the 2.0 version---which is to say not for a while yet).

Pandoc also allows LaTeX passthrough, so you could make use of BibTeX, which at this point has many more users, and most of the persistent problems solved.

The other lightweight markup languages with decent support for the needs of academic writing include MultiMarkdown, and ReST.

I'm doing my own thesis in org-mode in Emacs, which is working nicely so far. It's also a lightweight markup language with LaTeX passthrough, and a great interface for things like footnotes and document structuring. That said, it's not something you'd introduce a whole team of writers to. It's Emacs after all, which is still a bit of an adventurer's editor.