Who, pray tell, are you to say that different shapes and sizes and clays do not affect the flavor of the tea produced? Clearly, you do not drink good tea and you don't have an interest in it. If you did, then you would know better than to say something like that. Furthermore, if you are not yourself a tea drinker, why do you want to bother to produce teaware? Teaware made by american ceramic artists who don't even drink tea is invariably bad teaware. I know because I have seen plenty of it. When the maker doesn't understand or care for the purpose of the object he or she is making, then the resulting work will not be suited to that purpose.
I am one of these "tea people" you speak of. I came across your post during a random google search and then I joined this forum specifically so I could reply to you, because I am kind of offended by some of the things you said.
A lot of the current thought about the effect of different clays on tea has to do with the mineral content of the clays, especially certain iron compounds. This can be affected by the natural content of the raw clay, but also by the firing method. Japanese banko ware artists create purple clay by starting with red clay, firing it, and then reduction firing it. I don't know if Yixing artists use this type of method in particular, but they have many, many different firing methods that produce many different results. Google "yao bian" to see examples of my current favorite firing method. Various methods similar to this can produce varying proportions of Fe+2 and Fe+3 and other things which later affect the water chemistry when tea is brewed. It is very difficult to find published studies about this sort of thing since they wouldn't be in English anyway, but what I am saying is that the presence of some mineral compounds in the right amounts will have an effect on the solubility of some flavor oils in water. The interior surface of purple yixing pots in particular are often very porous so that their surface area is many times larger than the dimensions of the pot. Because of the large surface area, the reaction speed is greatly accelerated for any catalytic reactions that may be affecting the chemical properties of the water and, by proxy, the tea.
For a similar reason, it has become a popular practice among tea drinkers in china and elsewhere to use a Japanese tetsubin kettle to boil the water. We do this because tetsubins are made of rough cast iron with no protective coating. They are only steam baked to prevent rust. The accumulation of mineral scale from repeated use helps protect the iron too. Boiling water in a tetsubin actually adds iron to the water and this affects the flavor of the water directly in addition to it's effect on the solubility of flavor oils in said water.
To your credit, I don't think that there is necessarily anything all that special about the clay from Yixing, at least not before it's processed. It comes in different colors, each with different mineral content, but all with a lot of silica/mica and iron compounds. However, the processing that has traditionally been involved to create such a porous inner surface is extremely painstaking and it has changed a great deal since 1959 when the process was first automated to include machines that could crush the clay ore to a much finer grain. Originally, it was all done by hard physical labor, pounding the clay with mallets in a hollowed out tree trunk, etc. see http://terebess.hu/english/yixing1.html for the beginning of a great summary of 500 years of history of the art you seem to think you can imitate.
I recommend you get a look at a book called "The Art of the Yixing Potter". It is a large and beautiful but sadly out of print book that has hundreds of very large detailed photographs of many very old, artistically significant, and famous Yixing teapots from the collection of the K.S. Lo Museum in Hong Kong. It is a rare example of a book on this subject whose text is in both English and Chinese. This book also contains probably the most factual account of the history of tea that may be found in english, citing scholarly translations of very old chinese texts about how tea was cultivated, prepared, and consumed in different ways throughout different periods in history. I have a copy and I will be happy to show it to you if ever you find yourself in San Francisco.
I recommend you look at what ceramic artists are doing with teaware in Japan, Taiwan, and Malaysia, because these places all have strong tea cultures.
Finally, I recommend you watch this video of an Yixing master demonstrating some of what he does for a British audience: http://www.essenceoftea.co.uk/blog