This very convincing and beautifully made (especially considering it is the work of an individual/circle) Touhou OP style anime has recently appeared, and looks to be a MAD to whet the appetites of fans for an eventual anime.
It seems inconceivable that a series of such popularity will not eventually get an naime adaptation, eventually.
Zun’s statements that a Touhou anime is unlikely due to the difficulty of a such a project being doujin in nature, or due to copyright concerns, keep being raised with regard to this.
I am instead rather convinced that he is biding his time; eventually a studio will offer him millions of dollars if the popularity of the series continues to increase (a doujin anime would likely be non-starter – where would the seiyuu, etc, come from?), and at that point the copyright concerns can be done away with easily enough.