I suspect that Quicken users who download data (with the exception of those who use the Web Connect connection method to download) are going to be increasingly encountering FDX as time passes.
Schwab users, for example, are already dealing with FDX, since FDX is the new standard for pulling data from financial institutions for downloading to financial software. Quicken's mechanism for handling FDX is Express Web Connect+ (EWC+).
The two primary benefits of FDX are said to be: enhanced security (better than not only Express Web Connect, but better than Direct Connect * ); and the elimination of any need for "screen scraping" (which at its best is problematic, and is constantly under the threat of being broken by having the financial institution change the format of their web site).
FDX will employ an expiring "token" (authorized by the customer/user) to access the financial institution data - rather than the customer/user User-ID/Password.
FDX will use a non-proprietary API to select the accounts, and the items of data from those accounts, to be downloaded.
As I understand it, Quicken itself will not be employing FDX directly as Quicken will not be accessing the financial institution's FDX data directly; Quicken's aggregator, Intuit, will be the one actually dealing directly with FDX. But the data Quicken receives will, apparently, no longer be in OFX format.
The Quicken OFX Log has not contained data from Express Web Connect downloads for some time now: that will remain true for Express Web Connect+ as well.
Given that FDX appears to have better security than even Direct Connect; and, it appears likely, will be cheaper than Direct Connect: my guess is that more and more financial institutions will be switching to FDX - and that will mean more and more Quicken users will be employing EWC+ to download.
[ (*) After composing the above, I have been told by a knowledgeable person that the same security approach being employed by FDX, can also be used by OFX. The newest OFX specs specifically allow for the same security approach as that used by FDX. Meaning that Intuit/Quicken can choose to make Direct Connect as secure as FDX ... though possibly not as inexpensive as FDX.]
Here are current FDX members: