The Xiaomi Mi Max 4, as well as a possible Pro variant for this phone, had been rumored for release. However, Lei Jun, the OEM's chief executive officer (CEO) has contradicted this on Weibo. It now seems that any devices of this line, in addition to the Mi Notes, have been axed, for 2019 at least.
https://www.notebookcheck.net/No-Mi-Max-4-this-year-Xiaomi-CEO.425852.0.html