Photo mode does look like a good bit of fun! I caught it today for like almost an hour checking out those options. It looks like it has everything that would be needed for a portrait suite that actually works, except it's missing that last step to spit out a portrait that can be used in-game.
Right now all the portraits for custom PCs are very samey samey, it's because the colors and facial expressions can't be changed there. The colors available are mostly blues and grays, a couple purples and greens, but definitely missing life half the rainbow. Plus they're gated by the Character's race. But now we can do all this extra stuff with dozens of poses, switching the weapons around and the jazz hands etc. Seems like it would work really well
I can imagine 2 main uses for photo mode in-game. The first to make an individual character portrait, the second to make a party portrait.
For the party portrait it would be fun to do like one for each Act and then they play in a montage at the end or something. That would be a riot probably! hehe
