I know there are Shi-hans that are not Japanese, and the contention of that in this discussion. Maybe understanding why there is more non-Japanese Shi-hans might have a deep rooted cause reflected by this story. Things may not be intentional, but result from an attitude long held by the Japanese they are not aware of.
A Woman and the Bell of Miidera
In the ancient monastery of Miidera there was a great bronze bell. It rang out every morning and evening, a clear, rich note, and its surface shone like sparkling dew. The priests would not allow any woman to strike it, because they thought that such an action would pollute and dull the metal, as well as bring calamity upon them.
When a certain pretty woman who lived in Kyoto heard this, she grew extremely inquisitive, and at last, unable to restrain her curiosity, she said: "I will go and see this wonderful bell of Miidera. I will make it send forth a soft note, and in its shining surface, bigger and brighter than a thousand mirrors, I will paint and powder my face and dress my hair."
At length this vain and irreverent woman reached the belfry in which the great bell was suspended, at a time when all were absorbed in their sacred duties. She looked into the gleaming bell and saw her pretty eyes, flushed cheeks, and laughing dimples. Presently she stretched forth her little fingers, lightly touched the shining metal, and prayed that she might have as great and splendid a mirror for her own. When the bell felt this woman's fingers, the bronze that she touched shrank, leaving a little hollow, and losing at the same time all its exquisite polish.
From, F. Hadland Davis, Myths and Legends of Japan (London: George G. Harrap and Company, 1917), pp. 141-142.
Maybe they feel parts of Aikido as a martial art, as a cultural thing are very sacred that if Aikido is full of non-Japanese Shi-hans if touched would diminish, leaving Aikido a little hollow, and and losing all its exquisite polish.
And as unfair as it seems, no where does it say in Aikido they have to adopt affirmative action. I don't think O'Sensei opened up Aikido to the world thinking any body, but
Japanese where going to run it. He did follow traditional Japanese martial art hierarchical ways pasting the art on to his son, who passed Aikido on to his son. And for Japanese the governing body of Aikido is pretty liberal in this sense. I think that should be taken in consideration when taking Aikido which is a Japanese art. I mean I don't ever see a Japanese born national ever being the President. And I don't ever see a non-Japanese ruling Japan (unless by force) as Emperor of Japan no matter how many non-Japanese live in Japan. These things have to be consider part of the territory at that level of Aikido. Most people, will never be or want such a level as Shi-han. It makes me wonder though why some do.