After hitting up friends and family, I have initial survey results for Trigrams.
The most striking result is trend on whether to have a full 8-suit deck or split the cards into 4-suit decks Right now, the prevailing thought is offer a 4-suit pack (core suits of Water, Heaven, Fire, Earth and offer the other 4 suits as an expansion pack.
Other trends include using a character-based back instead of a more abstract one, and going dual-language with both Korean and Chinese.
As of now, the choice of card size is a little more split. Most with a definite opinion favor the traditional Poker size, but’s about a 55-45 split (when giving half of the ‘either’ category to each specific size). Going the traditional size does open up the ease and variety of producers, and could reduce costs a little. More to come on that.