Watch This Space, page-1987

Brad has said multiple times the ultimate goal is EVERY credit card GLOBALLY so Discover is the remaining of the big 4 known providers...and all of the other providers (union pay) plus more is the goal to eventually be there. Do not see the need for all merchants in the future to list all these in the checkout although available. "All cards accepted" blanket statement would be simple.

I therefore do not see any indication that AMEX has anything to do with a funding facility. Wouldn't the facility need to be bigger than AMEX alone in the future to fund all card transactions globally? Multiple facilities from multiple providers most likely will be needed.
Nor do I see a requirement for any further dealings or pilots with AMEX is required now. If VISA pilot is successful they can just deploy what they have learnt at scale to all the others globally.

AMEX is a tiny tiny piece of glabal puzzle.
Just my thoughts.