That tweet is unofficial, and yes, is from the livestream I talked about: the translation is not 100% correct, because in the livestream they said that they were considering a PC port and there was some initial planning, but no actual development started. It's a little different compared to what is written in that (unofficial) tweet.
Basically, they were ready (and are still ready), but there is need of approval from the upper management. When you read latest financial Sega reports, you'll see that Project Sekai is still very popular, so it makes sense why is still in the mobile devices and not being ported to PC/console.
I'm the first that would love a PC/console port, but I also understand why the upper management still haven't approved it. When your game is still super popular (at least in Japan), and there are many concerts, events, goods, .. it's difficult to make that decision. Other mobile games are being ported to PC/console when the popularity starts to decline, but Project Sekai, since is supported by both young fanbase, Project Diva fanbase and Miku fanbase in general, is still very strong.
Basically, they were ready (and are still ready), but there is need of approval from the upper management. When you read latest financial Sega reports, you'll see that Project Sekai is still very popular, so it makes sense why is still in the mobile devices and not being ported to PC/console.
I'm the first that would love a PC/console port, but I also understand why the upper management still haven't approved it. When your game is still super popular (at least in Japan), and there are many concerts, events, goods, .. it's difficult to make that decision. Other mobile games are being ported to PC/console when the popularity starts to decline, but Project Sekai, since is supported by both young fanbase, Project Diva fanbase and Miku fanbase in general, is still very strong.