Oh yeah, I've seen those one-handed dual controls in catalogs but I hadn't considered them for a trike...should work, yes!
Long-time Coventry Cycleworks fans, here. That's where the EZ-3 came from and that's where I'll go when I eventually get around to a test riding a tadpole. I haven't seen a trike with a diff in it but I have heard they exist. I've also heard they are expensive, and some other downsides. I think a dual freewheel system would cost less (at some production volume), be lighter and more maintainable, and it directs power to either or both wheel with traction, unlike an open diff..but maybe trike diffs (planetary?) have some sort of "posi"??