According to the official website, ufotable announced a collaboration anime project of Anime Tenchou and Touhou Project. The anime will be shown at Animate Ichioshi Bishojo Anime Matsuri to be held on November 20th.

Anime Tenchou 10th Anniversary official website
Key Illustration of Touhou x Anime Tenchou

It's one of the ten projects to commemorate the 10th anniversary of Anime Tenchou. A new promotion anime of the manga will also be produced by ufotable.

Sources: Kondo's tweet, ufotable official website

Updated on Sep 25th
Zun tweeted that he is not involved in the production of the anime and he considers it to be a secondary creation.

Sources: Zun's tweet 1, tweet2

Updated on October 11th
A trailer of the anime was shown at Machiasobi vol.4.
Anime Tencho x Toho Project Trailer (Youtube)

Source: GIGAZINE