We're a really smallish company. There would be about two people learning the new technology
I have considered the XML formats before. Even MS Word's new formats are a compressed XML internally and can be somehow stored in Mercurial (which we use) as such. There are still some binary files in the ZIP produced by MS OFfice, though. Perhaps LibreOffice would work better in that regard. I'm still afraid, though, that some editing actions might cause "global" changes to the file, making merging (yes, I'm aiming at merging) really difficult. Writing in LaTex, on the other hand, resembles programming (or so I've understood) and one has direct control over the content of the document (in a GUI editor, the control over the content is indirect). One could even pay special attention to make changes that would be easy to merge.
Additionally, our documents are loaded with formulas and equations. If we learn to use TeX equations, copying, editing or even searching them would be much easier.
Thanks for the pointers to the LibreOffice, though. If we don't switch to LaTeX after all, perhaps the LibreOffice uncompressed XML format would serve us well.