Technically, Miku's always been controlled by a real dancer through motion capture (I know that Exemplar linked to an article a long time ago that I translated a bit about before, but I can't find it anymore. It was about the girl who made Miku's dance routines. I imagine Sega had her do the mocap, but I can't remember her name. I tried looking it up, and Yui Ogura did the mocap for Project Diva and Project Diva f, but I don't know about the other games or if she's the one who came up with the dances).Personally I'm a bit opposed to the idea of real time control, maybe for the MC parts is good, but I somehow dislike the thought of Miku being controlled real-time by some dancer. If said dancer were to make a mistake or something, it would be instantly reflected in Miku's dancing too, which I think would be a bad thing, not to mention the exhaustion of a live dancer you pointed out.
We're so used to Miku performing the same dances flawlessly over and over again and not getting tired during live shows. I don't know if fans want to see that "human touch" in her movement and possible mistakes a dancer might do.
I have been thinking about if they would ever switch to fully real-time songs how I imagine they'd achieve it. Personally, I think they would have more than one dancer ready to be motion captured. (Kind of like how interpreters switch with a partner every half and hour-ish at the UN.)
So even if Miku is a hologram, her dances weren't "hand animated" from scratch by animators, it was mainly mocap with some tweaking on parts that didn't record right. There are tons of professional dancers who do seemingly impossible dances (like Kpop stars or like... Lady Gaga backup dancers), so saying they would make Miku look bad is kind of harsh and slighting the dancing profession. I also find it hard to believe that people watching would be like "Oh, this dancer screwed up, Miku's hand should have moved at this height a few seconds ago, the performance is ruined!" I could only imagine it being ruined if the performer collapsed or the mocap suddenly setup failed or something.
I'm sure that part of their plan in having the real-time voice conversion and the real-time mocap is so she can like, run up on stage and give the audience a unique greeting through her poses and words or interract with musicians she's collaborating with. (Because dance routines and clips of Miku talking to the audience take a long time to render and animate compared to the tech for real-time VTuber type stuff.)
Sorry for rambling a lot. I thought what you wrote about the event was interesting, I bet you got tons more photos and what you shared was a fraction of them. And you even got to do cool stuff in Japan that wasn't exclusively being at the concert venue. (I guess it's hard for me to imagine the scale of such an event and what it feels like being there because I've never been to anything like it, but I think it must also be hard to fully convey through words/pictures what being at a Miku event is like.)