The client contains our most sophisticated code. It's also the most important from a trust perspective, it is responsible for securing your data, our servers cannot see anything of yours because of the client. So it's vital the important parts of it are open source.

That said, I'd like to open source a server. We need a reference implementation of our control protocol so it can be properly analyzed by security experts. Not sure what form that should take yet, but I'd like it to be usable.