So, uh, while I'm writing about concerts I should probably talk about this one. For the very very small handful of people who care.
I went to it!
It was pretty neat.
Definitely unique among any game music event I've been to, this one felt very intimate. It was a small group of performers in a relatively small venue. The orchestra sat in front of a large video screen, where we were greeted by nothing but the title screen of the game as we walked in. One guy was the player, and he sat down with a PS4 (I think? I couldn't tell if it was PS3 or PS4 from where we were sitting... doesn't matter in the front and center of the audience by the conductor.
The "concert" went approximately as one would expect. The player played the game and the orchestra adapted the score to his actions as he went. The guy didn't do anything particularly crazy or loiter in any one area too long so there was nothing particularly weird about it. If you know the music/game you know basically what this was. Another player did join in via the game's network feature, and it was REALLY cool watching the two interact in this sort of setting. The audience reacted appropriately, gasping at close encounters and whatnot. The whole thing took a bit over two hours, about as long as a normal playthrough of the game would take. They even had a vocalist come out just for the ending theme (actually I think she was sitting there on the side of the stage the WHOLE TIME biding her time).
After all was over, I talked a bit in the lobby to a few of the performers, who offered some insight into how it came together. Their scores were on iPads on the stands, and they had custom foot pedals that could advance the score to the next page or return to the previous page as necessary. All of the performers had actually played the game (I smiled at the story the one told about how one of the others told her "YOU HAVE TO TRY THIS GAME" and they played through it together - reminds me of how a lot of people came to experience this game). They also were acutely aware of just how annoying this performance could be depending on the player - they knew nothing and the instruction to him was just "start" with no further demands. One of the performers said she was especially glad the guy didn't fall off during the snowy sequence because that's a pretty demanding and VERY repetitive bit of music if they'd had to keep on playing it forever.
All in all, I'm really glad I went to this event. I love the game Journey, and I love its score, and this was a totally unique and different VGM experience that I'd like to see more of in the future!