Release early and release often. I can't wait to try your app. I've been wanting to play zendo for a long time, but wasn't willing to pay for all the sets of pieces that it seems are required now that zendo is out of print.

In terms of generating rules, you might want to look at CopyCat and its algorithms for analogy solving. There is an excellent discussion of the strategies it uses in the author's recent Complexity: A Guided Tour. You'll certainly get lots of good ideas for rule generation by looking at the discussion in that book.