Google Photos looks to be getting a Portrait Mode adjustment feature in an upcoming update to the app, as data found in the latest APK version suggests that Google wants to enable users to tweak the bokeh effect that gets added to photos with Portrait Mode. Once added in these controls will let users either intensify or soften the blur effect that ends up being added to the background subjects in an image, so if users only want to blur things out of focus by a small amount it appears they'll soon be able to do so. That said there's no clear distinction of when Google will actually add this change so it could be in the very next update or it could be further out.
Google is also going to be adding a color pop suggestion feature it looks like which will essentially be just as it sounds – the ability to add color pop to a photo to enhance the color in it and make it more vibrant. This feature has been rumored before so it's possible that Google is preparing to add it fairly soon. If you often use photo books and have wanted to add captions to them, you might be getting the chance soon as well as Google seems to be adding this feature at some point in the future as well.
What might be the most useful upcoming feature, at least for those who find themselves running out of storage in the Google Photos app, is an ability to recover some of that storage not by trashing some of your old photos, but by downgrading the original quality images to high quality, letting you keep those images instead of having to delete them but at the expense of losing some image quality in the process. Chances are that most people will be able to find some pictures which they might not mind losing quality for if it means they can open up room for more pictures. If you use Photos often, look out for these new feature in the near future.