The debugger canvas is an interesting way of displaying multithreaded debugging. It's not very different from parallel stacks and I guess that parallel stacks was the inspiration for creating the debugger canvas.
What I could really need as a developer, is however a much simpler solution: To be able to debug the thread I'm currently looking at and ignoring all other threads. This would allow me to continue stepping down the path I'm on without being interrupted by other threads stepping down the same path.
Usually, when I'm debugging, I'm not focusing on what every thread does (Focusing on too many things cause information overload). Instead I'm focusing on what my current thread is doing and it would be very nice to be able to do so, without my focus being moved to what other (And to me irrelevant) threads are doing.