This is exciting, but...

is it crazy heretical of me to say that I'm doubtful even a software implementation designed by David himself could fully capture GTD?

I dislike implementation tools as a general rule. You can teach GTD to twenty people and each one, based on his or her needs, will implement it in an entirely different way, and in ways that are 100% consistent with the overall thought process. I often find a single implementation tool causes people to focus their energy on understanding the tool rather than

collect
process
organize
review
do

which imo, should be at the center of anyone's implementation.

But I look forward to seeing what comes out of this partnership. I'm sure it will be great; but I'm pretty sure I won't be running out to switch my system to it right away.