I guess a digital bible complete with a glossary and dictionary on blueprints wouldn’t be a bad idea for the marketplace. it’s the next to best thing having all the tricks of the trade. there is one major problem to this though; the number of updates to UE4. I spent 3 months watching a whole bunch of video tutorials and had to quit most of them, because of how everything has changed in the later versions. In fact a large portion of vids on youtube have become a bad source for blueprint learning, resulting in lots of questions.
whoever tackles the digital bible of UE4 should be flexible enough to updated it when necessary. otherwise it’s a antique purchase.
For other marketplace ideas. some more genre type templates would be great for indies. blueprints remain a heavy topic and accounts for a huge portion in all projects. more blueprint related subjects i think should be in the marketplace. IMO art assets don’t nearly take out as much time from game development as scripting does.