We don't have any hard data - this is based on our personal vision, and our understanding of our user base. People mostly use ShareLaTeX because: 1) There is no installation, 2) You can access it anywhere, 3) You can collaborate easily and effectively without needing to be technical and know git/svn/etc. I don't think being open source will threaten any of those points, but it will make ShareLaTeX accessible to the large group of people who want to run a local version but haven't been able to so far.
It will be interesting to see how things look in a months time. I'll try to post an update!
Please do post an update. I have a side project I'm starting that will be a paid service, but I'd like to AGPL it in keeping with the free software philosophy.
It will be interesting to see how things look in a months time. I'll try to post an update!