I thought about that, too. The thing is is that after 6b during a block string there aren't any moves that cancel other than 623c or vivace itself, if your opponent knows Carl's gatlings they will know that it's safe to act, defeating the trick.
Blah, I don't know it's all theory really, I'll have to test it out when I play my friend again.
Edit: I was also wondering how 2c's new fatal counter properties could be utilized.
Consider the following:
Let's say that near the corner I do an air combo ending in 214c near the corner. If I 8d after the combo (to prevent them from teching out of the corner) they are forced to go straight down right? Well if they are coming down with an attack, like Litchi's j.b which has a good hit box below, would it trade with 2c, or would that get me a counter hit? If it would, what kind of stuff could you follow it up with?
Here's one idea:
2c, FC, j.2c allecan, land, j.2c allecan, j.c, j.2c, j.c,dj.c, j.2c, j.c, 214c. I'm not sure how that would prorate, but I know that j.2c does a significant chunk early-combo, and tacking on 623d in the middle wouldn't be a bad idea.
Ugh, so much stuff to test today.