Incorrect. I had 13" MBP --> Apple T-bolt display --> Pegasus Raid T-Bolt --> Apple Cinema Display.
In the past before I used the cinema display I used a miniDisplayport-> DVI to connect to a 22" Dell ultrasharp.
You just can't go from t-bolt display directly to miniDisplayport.
I'm not sure what you mean. You can plug a mini displayport cable directly into the machine. You just can't insert a mini displayport device with the intention of running other devices off that one. I have a mini displayport to displayport cable around here somewhere, so they do exist and work if plugged into a thunderbolt port.
List the Apples with ExpressCard that could potentially use such a dock.
Very short list.
That isn't the only problem. Many express cards aren't sold on high margins. They're typically Windows only or Windows + OSX compliant. The number of supported products under OSX has decreased significantly. Snow Leopard to Mountain Lion alone killed support for a lot of them.