The latest leak is from reliable tipster Evan Blass which shows images of Wear OS 3.5 with One UI Watch 4.5 on top. This software is going to be pre-installed on the upcoming Galaxy Watch 5 series. The biggest feature leaked is a new QWERTY keyboard from Samsung, you will be able to use swipe gestures too on this keyboard. Then we have some accessibility features like adjusting left/right sound balance, apply color filters etc.
The images also show that Dual SIM capabilities might be supported.
Aside from that the leaked watch faces shown are not so different from the ones came with current wearOS on Samsung Watch 4 series.