The Mi 5C was released earlier this year, with the lower specced variant of the Mi 5 featuring Xiaomi's own Surge S1 SoC. Information online points towards an Mi 6C being in the works. It is, of course, expected to be powered by the Surge S2.
https://www.notebookcheck.net/Details-of-the-Xiaomi-Mi-6C-revealed.258262.0.html