OWC is a company that caters to iMac fans who want to upgrade their new Apple all-in-ones. It has announced its new Memory Kits for the 2019 27-inch iMac (the 5K model). As this new 2019 variant has 4 user-accessible slots, OWC is also currently testing out the possibility of maxing its RAM to 128GB.
https://www.notebookcheck.net/OWC-has-prepared-RAM-upgrades-for-the-27-inch-2019-iMac-already.414796.0.html