Conducting a google hunt for terms related to my research on space and place, I've come across Lee Sheung Hung's 2007 University of Hong Kong thesis, "To Write the Unwritable: Contesting Dung Kai-cheung from Within," which confirms that another author has used the word "omnitopia" in published writing -- but in a manner unrelated to my own work.
Lee Sheung Hung's thesis examines the works of Dung Kai-cheung (cited in other publications as Louis Dung Kai Cheung, Louis Dung, and elsewhere as Dong Qizhang), author of The Atlas: Archeology of an Imaginary City, a future history of Hong Kong that was published in Taiwan in 1997.
Doing some internet sleuthing, I found a terrific overview of The Atlas in Lingchei Lett Chen's Writing Chinese: Reshaping Chinese Cultural Identity (pp. 89-91). Here's a useful description of The Atlas from Chen's book: "The author claims that the Hong Kong that is known to its people in fact cannot be pinpointed on a map because a map is only an 'epistemological translation' of the world" (p. 90).
Of particular interest to me, Lee Sheung Hung reports that Dung Kai-cheung uses the word omnitopia in The Atlas, albeit in different manner than my own articulation. In The Atlas, "Omnitopia" is the name of a brief piece that appears in a larger section entitled "Theory." According to a translation cited in the thesis, omnitopia refers to being "everywhere, and nowhere" (p. 23).
I can find no English version of The Atlas, other than Martha P. Y. Cheung's collection, Hong Kong Collage, which includes an excerpt, though not the section in which "omnitopia" appears. Fortunately, a friend of mine is helping me track The Atlas down; she's even offered to perform some translation for me.
Given the widely used nature of those root words -- omni and topos -- I cannot be too surprised to potentially find another theoretical articulation of omnitopia. I only wish I'd heard of this book before publishing my own work. That said, I am happy to recognize that I am not alone in working with omnitopia. I hope to chat with my counterpart beyond the Pacific one day soon.
February 4 Update: Dung Kai-cheung and I had a pleasant email exchange on this topic. He was gracious and understanding, a model of collegiality in a globalizing world. Given my enhanced appreciation for the author and the man, I continue to hope that the entire text of The Atlas will find an English translation. I'd like more people to read his articulation of omnitopia.