Hi and thanks for checking us out. Sorry that one isn't available yet. But yes, we will eventually have this keyboard shortcut (among others) added to the program.
I've personally tested all of those systems and my (admittedly biased) opinion is that GTDNext is far faster for entering in new tasks and projects. Moving via the mouse is also very fast, much faster than other systems. However, I agree that adding the ability to move items via keyboard would further increase the speed.