Multi-tonic Zheng 多聲弦制箏
The Multi-tonic Zheng 多聲弦制箏 (Duō shēng xián zhì zhēng) or Duō shēng zhēng for short (多聲箏) seems to have been made in 2011 by Professor Lǐ Méng (李萌), though my sources are not good.. It's effectively two zhengs combined; there are 21 strings tuned to the diatonic scale for the right side, with 16 additional strings tuned to the pentatonic scale on the left side. There is a tuning chart below. The range of the two sides is roughly the same, with the 21-stringed side having a deeper A and the 16 string has a higher D.
Source: Taiwanese store stmusic.com.tw.