It would be nice if we have the possibility to go to the next topic the same category with a shortcut. It’s really useful in case we have a category for just posting pictures and video, just use shortcut or one click, we go to the next one 
I hope someone find this useful as well. Cheers !
That’s kinda already available - the “Suggested Topics” box will favor threads from the same category. And if you start getting only repeats down there, just refresh, or go to the category’s page and scroll down until the first blue link. Because Discourse isn’t paginated, doing that actually isn’t very hard.
I agree that it’s easy to navigate back and choose the next one in the list. But in some cases, for example photos category which is a place for people to post photos. And people have an habit to skim through all images which may take about 2 or 3 seconds to look at an image, and go to the next one. I’d be a bit pain of navigating back and forth, if he/she surfs 30 - 40 images.
If you’re not seeing more topics from the photos category (for example) in the suggested topics, then there are no more new topics, or it’s a bug. Like @riking said, suggested topics is basically what you’re asking for. A “go to next topic” button would be the same as clicking the first topic in the suggested topics list.