Thanks for your quick reply. We are already looking at docs here, and we are also studying the source code.
I don't have a specific timeline to share, but we are pretending to make it live before the end of the year. (We will also need to develop some specific plugins for authentication and other integrations with our solutions)
Yes, we are using a homegrown comment system, django based (heavily modified), that is becoming outdated.
We will probably have no need to migrate old comments, since is a huge database (it is about 100M comments), and as we don't receive new comments on old content we could just create a static copy of it.
Mostly we would like to understand how redis and mongo are used, what could be cached and how all pieces of the software works together.