we have added an I/O expander on our Nordic Thingy:52 to increase the number of GPIOs from 32 to 48, see this Infocenter page. Specifically, we're using the Semtech SX1509BIULTRT, here is the link to the part on Digikey.
The firmware for the Nordic Thingy:52 can be downloaded from its product page, found here. It will contain some source code showing you how to interface the SX1509BIULTRT with the nRF52832.
