You don't necessarily need a differential on the back of a delta, you can just have one driven rear wheel (may sound odd, but simpler versions of the Hase Kettwiesel use this arrangement quite successfully)
For those thinking that trikes implies slow, note that the LEJoG record is actually held by a (recumbent, fully faired) trike.
I know all about the steering differences, so every time I try one I tell my self over and over not to lean but to steer, not to lean but to steer, not to lean but to steer, and end up drifting down the camber in to kerb in short order. I do get there after a few goes, but it's surprisingly tricky to "unlearn" bike steering for at least some of us!
Maybe I missed it in the previous page, but there can be issues getting them on to trains. There are folding recumbent trikes that will get you around that, but any sort of transport by another vehicle is likely to be more of a faff.
Often seen riding a bike around Dundee...