Descending order of priority.
* Why did you decide to change the designs of Reimu and Marisa from Shuusou Gyoku onwards?
This is probably the big one.
Questions on the finer points of Touhou canon (may or may not be suitable for a press interview, but if someone is willing to, ask them during the panel instead?):
* What is the basis of the season numbering in Gensokyo? In particular, what is the relation between the season numbering and the creation of the Great Hakurei Barrier? In addition, when does the season number change?
Two things that are suspected but never confirmed.
* In the newspaper article of PMiSS about Akyuu's birth the photo features a young girl. Is the girl Akyuu? If so, was she actually born at that time? If not, how does the girl relate to the article?
Asked by Fonzi above, but first pointed out by cuc over a year ago.
* Was Remilia in Gensokyo during the Vampire Incident?
Might as well ask. After all, for some time it was claimed that Remilia entered Gensokyo after said incident, citing Akyuu.
I'm sure I had more - I knew I should've started a text file for this.