I ended up applying and getting approved. The process was straightforward, but not "quick and simple" like a standard 60-second decision USA card application. Here is a detailed step-by-step account of the process and timeline that I originally posted on FT for all interested:
I just wanted to share my very recent experience applying for a Platinum ICC (dollar) card (the one serviced out of the UK), as information about the process isn't as prevalent as it is for other cards and regions:
To preface and for context, I am a U.S. citizen and currently hold U.S. Amex cards (since 2003), but reside abroad in a non-excluded country (i.e. non-EU, non-Singapore, and obviously non-U.S.).
April 21: I submitted the online application and used one of my U.S. Amex cards as proof of eligibility (i.e. having an Amex card for at least six months prior to applying). I applied for a free Platinum supplementary card (as they deem Authorized Users) for my wife in the same application.
April 26: I received an automated e-mail stating that my application was being reviewed.
April 27: I received a personalized e-mail from a real person updating that the application was still in review, and they were awaiting information from Amex USA about my existing relationship.
April 28: The same representative sent another e-mail requesting a copy of my ID or passport (no certification required), my wife's ID/passport (certification required), and a copy of proof of address from a list of acceptable bills/documents, such as utility bill or municipal tax bill (no certification required). I was also asked to sign a form stating that I did not reside in the United States and was aware of the fact that the card was not on offer to U.S. residents (no certification required).
The certification isn't a difficult process and does not require a notary or apostille: there is a form with a list of acceptable professions that can sign off on the certification (e.g. lawyer, doctor, postal worker, civil service employee, accountant, etc.). My biggest issue was finding someone who was willing to listen and understand what was needed and not think I was trying to somehow defraud them or make them commit to a financial obligation (somewhat understandable since the form was in English and from Amex, not from a local entity/language). I sent the documents that didn't require certification the same day and asked to put my wife's card on hold in order to not delay the processs.
April 29: The same representative confirmed receipt of the documents, and that she would proceed with my card only to prevent processing delays. Since my proof of address was not in English, it would take around 72 hours to have it translated and confirmed (at their expense).
May 4: I managed to have my wife's ID certified and sent it to them asking that her card now also continue to move forward in the approval process.
May 5: E-mail received congratulating me on being approved (along with my wife's AU card), and that the card and PIN would arrive in 7-10 business days. I was told the Priority Pass could be requested only after receiving the card.
I contacted the call center a few times during the process with questions and to verify receipt of my e-mails (they don't have an auto-reply set up verifying receipt), and the representatives were always UK English speaking and extremely patient/polite. No hold time at all, ever. In fact, by chance I even spoke with the same representative that processed my application on one call, so I have high hopes that the service will be very intimate and personal.
I'm not sure why my documents and proof of address didn't require certification (perhaps due to the 18-year relationship with Amex USA). Also of note - I was not required to provide proof of employment/income or proof of the bank account I provided in the application, which, according to past reports here, seems to not always be the case with all applicants.
Hope this helps someone and provides a clearer picture of what to expect when applying for an Amex ICC card!