The Xiaomi Mi Max was launched in May 2016, featuring a big 6.44" display and the Qualcomm Snapdragon 650 SoC, while the Mi Max Prime bumped up the SoC to the Qualcomm Snapdragon 652 SoC. The highlight of both these devices was the large display, housed within an even larger body from an era when OEMs didn't race each other to cut down bezels wherever they could. The Mi Max unapologetically targeted an audience that preferred large phones, and as such, it did restrict its scope to an inherently smaller niche at the time.
Alas, all good things must come to an end, and so does the Mi Max. Just a while ago, the Xiaomi Redmi Note 3 received its final MIUI 10 stable update, and now, it's the Mi Max's turn for the same. As Xiaomi notes in the announcement post, the Xiaomi Mi Max and Xiaomi Mi Max Prime have received their last MIUI 10 Beta with the release of version 9.2.28. There will be no more MIUI Beta releases for these devices.
Consequently, Xiaomi is preparing a final MIUI 10 stable update for the two devices. The MIUI 10.3 stable update is expected to be released in April 2019 for both these devices. Users on the Beta can choose to remain on the beta, or they can migrate back to the stable channel to receive the upcoming final update.
The Xiaomi Mi Max is succeeded by the Mi Max 2 and then the Mi Max 3. Despite the rather niche nature of its audience, Xiaomi seems to remain committed to the big screen device. While I do not personally see myself purchasing a device in this lineup in the future, the people who prefer huge phones will be happy with the existence of this product lineup as their potential purchase.
Thanks to XDA Senior Member zombiezoom for the tip!