Hi Jono,
I see your point, but doesn't it make working with these kind of lenses somewhat unpredictable? Or do you, with experience, develop a feeling for how the lens will fit or draw a certain scene, so you might take advantage of its character?
While I generally prefer lenses with a flat field, I'm trying to figure out why Zeiss has chosen this particular design in their WA ZF line, and if other parameters may have been optimized for this trade off. That's why I'm interested in users feedback to learn how they handle them.