I've just installed the gallery app to see how this could work out for my forums. I have a lot of topics that are 'what did you eat today' or 'show your new purchases' in which members post pictures. Asking them to first upload that to a gallery, then go back to the topic and insert it as an image is just too much hassle if you look at it from a user perspective. Of course as admins, we would want them to do that, but reality is that people are used to post image links or just add a photo from their smart phone and dump it in a topic.
I would really like to be able to curate this content (even have a setting that would allow me to download images from external links and add them to my own media database). For instance to be able to display a masonry grid with all images posted in the forum. Showing off this content is a great visual and appealing way to show off forum content, which may then again drive visitors etc.
I am not sure whether the gallery app in its current form is the way to go for me (at least, I do not see the use case), now that the forum topics are really used as the content container.
I think this is a great topic, looking forward to hear your views on gallery / image content curation and the forum software.