To the OP: don't give up yet.
A few days ago I successfully booked upgrades using SWU's on an AF- operated TATL roundtrip in September on a DL "W" fare.
I had been reading the posts on Flyertalk about the changes in the SWU rules and that AF "A" fares could no longer be used and had the same problem the OP did -- could only get "A" fares in PV on AF site.
When I tried "M and above" on DL.com I got "W" fares at a reasonable price but it wasn't clear to me that a "W" DL fare would work. In a couple of Flyertalk threads people asked specifically if a DL "W" fare could be used to upgrade with SWU's, but it was never definitively answered.
I called DL a couple of times to specifically ask if a W fare on AF-operated flight could be upgraded with SWU's -- and got agents who did not seem to understand my question.
So I found flights with O availability showing on EF, chose "M and above" on DL website -- ($1800 AI with Y domestically and W TATL) but was unable to purchase online (got that "sorry, call us" screen). So I called DL and got a helpful and knowledgeable agent who knew exactly what I was trying to do and went right ahead and booked the ticket and processed the upgrades.
My itinerary now shows me in BE seats and the AF website does too. So I am assuming this did work. (If someone out there with more knowledge sees a problem here, please speak up!)
Agree this is very confusing and the DL written rules are unclear -- But my advice is to keep trying until you get an agent who thinks it can be done.
I hope this is true. Being able to upgrade from AF A was a great benefit. I guess if you do the booking on the phone, and the ageny subsequently says that they can't confirm you into O (assuming O being available), you should be able to cancel the ticket...seems like a low risk approach to me.