Sorry for double posting! I tried to edit my post but...took too long it seems!

A Triamese is not just hooded. It pertains to all white marked Siamese btw.

The problem with a Triamese or white marked Siamese is that they change during shed, are random and it would be difficult to judge the patterns.
The original intention for breeding a Siamese is to create an elegant gradient complimenting the darkened (colder) ends of the animal.
It's meant to be smooth and streamlined. The Triamese, while still fracken adorable, disturbs this greatly and defeats this ideal and follows none of it's own. I don't think it's that the clubs won't change because they don't feel like it, I believe it's because the Triamese is still very random and no one really knows how to judge it other than build. It's very difficult. Im all for it though, that's just my thoughts on the clubs. :B