I didn't notice earlier cause of HoloGTA, but Mio confirmed a few weeks ago that Blue Journey is officially cancelled as of now:
It basically didn't do as well as management wanted so it got axed. Mio said she would have liked to do another one, especially for the fans that loved the concept. She feels that if they did, it could have gained more traction and been more successful, but she understands that there are various circumstances (money) to consider. While it is over for now, she hopes that management doesn't give up on these sort of group projects and that they'll do them more than just once.
And here's an EN clip of Lamy expressing the same sentiment a few days later:
I get it but still, it kinda sucks to hear after they hinted at a sequel multiple times. The Blue Journey live/album was incredibly unique for a Holo project and one of my favorites of last year. For Subaru, it was a very big step on her idol road as it forced her to go out of her comfort zone and sing in ways that she have normally never done. She was thankful for Blue Journey because she could feel the improvement she got from it in almost every performance afterwards.
Thanks for giving us some amazing songs and this great outfit