Welcome to the non scale guys!
If you've tried to run an SCX10 at anything above 10mph, you'll understand why open diffs are not really needed on a scaler. Barrel rolls are in the forecast regardless of the axle settings. I think it's a neat feature, but what happens in a 1:1 does not always translate into 1/10. A slight overdrive on the front axle will help the turning as much as an open diff and keep the costs down.
Having said that, I have a 3-speed truck with 2/4 wheel drive capability - I like gimmicks. Makes the trail more interesting.
I spoke to Tower on Friday and asked if they had order info or a timeline yet. They do not. In fact, they have not heard a peep from TRX about it.