A bit off topic, but I'm glade to see a project like this running there own instance of matrix instead of the usual centralized/proprietary/censurable solutions.
We never broke ties with IRC though. You can still join #reactos or #reactos-dev on Freenode, both are bridged to their corresponding Mattermost channels using Matterbridge.
Our Matrix server was set up right in time for FOSDEM 2021. It will soon be extended to bridge to the IRC and Mattermost worlds, as Matrix integrates even better with Freenode's IRC server than Matterbridge.
As an open-source project, never place your bets on a single third-party platform!