I dont remember seeing anyone else post this but I just noticed that I am getting the option on the Amex website to shift CL between between credit cards online (in my case I had the option on my Hilton and Starwood personal cards).
This option was available near the bottom of my "recent activity" page on these individual cards.
I tested a $10K credit shift and it was approved and showed instantly.
This option is obviously not available on the charge cards and I didnt see it on my one business card.
(Note, I thought I saw this option a few weeks ago but I wasnt paying attention and didnt verify it at the time. So I dont know when this actually went into effect.)