That is an interesting idea for sure and Dropbox does provide a decent revisioning system where it keeps track of all files, kind of like how Git does it. The biggest issue would be ensuring you and the other person are always in sync with eachother, and I think Git would be the best option for that. We haven't done any work on the Git feature as of yet but we are nearly done with the Dropbox backups,.
With that said when we are done with Dropbox we will discuss collobration tools with the main developer and get back to you. The core idea behind this plugin is to make backups consistent and to keep them in a safe location but if a few extra collobration steps are involved, that would certainly be a welcoming feature.