>>280494849
From my perspective, the main things holding up production are deciding who Ooarai’s 10th team member will be, what tank they’ll use, and how the story will justify Ooarai—with its rather underwhelming lineup of tanks—facing off against the overwhelmingly strong St. Gloriana, especially with Shimada Alice on their side.

Alternatively, it’s also possible that Bandai Namco is pressuring the actas to focus on other anime projects instead of Girls und Panzer, which could be another major reason for the delay in the das finale production.
(Ironically, the anime content made specifically for pachinko machines seems to be getting produced just fine.)