Samsung is working on Portrait Mode for a single Galaxy S8 camera and it may be able to enter through future software updates.
A customer asked if such a feature came in and few of the answers from Samsung Electronics support read: "no information yet, but we hope you will get portrait mode update with next SW". Usually response responses will only contain the first part, but this one not only suggests that the feature is possible, but also gives hope that it is just around the corner.
Note 8 has additional hardware; On the back of the device is a dual camera for natural portrait photos. Therefore, Samsung has to create some kind of software process to bring the feature to one camera setting in S8. This effort will not be a new thing because Google does it with Pixel 2, but Google has dual pixel technology in the new Pixels to help. And considering how well Samsung software is compared to Google right now, I'm not sure if you should have high expectations for this feature to work properly.
But rather jumping to conclusions too early, all this is not confirmed and we do not even know if Galaxy S8 Plus will get the same mode. But at least for now, it looks like portrait mode may be more pressing device.