Hi @solatic, Mattermost CEO here. If you have an on-prem HipChat deployment you want to migrate our team would love to discuss the possibilities.
Mail us at info at mattermost.com? // and this is an open invite to any HipChat users who want to keep data under IT control.
Regarding importing from HipChat, while it is tricky as the data is within HipChat's VMs and not documented, we can potentially work with you to move over smoothly.
The good news is if you switch to Mattermost we run as a single Linux binary with MySQL or PostgreSQL, so using us you have 100% access to your data as well as the source code to understand everything we do with the data.