An in-game tournament mode would have been deployed in Hearthstone, however, it only seems to concern Chinese servers and the Gold Series — the Chinese equivalent of the Grandmasters. The addon was developped by NetEase — Blizzard historical partner in China.
The community is asking for an in-game tournament feature for years, but Blizzard dropped the idea in 2018. Regarding recent incidents with Battlefy, one may wonder if Blizzard isn't looking for a new alternative. However, we can't be sure that this new feature will eventually reach European and American servers: for instance, the Replay mode was implemented on the Chinese server but was never introduced to Europe nor America.