Chinese sources report that Samsung has finished development for the 150 MP sensors and started work on the 250 MP ones. The first 150 Mp sensors are expected to launch with Xiaomi's flagship handhelds later this year, while the 250 MP sensor could arrive in late 2021.
https://www.notebookcheck.net/Samsung-starts-developing-the-250-MP-ISOCELL-mobile-image-sensor.463232.0.html