Well, I was right.
Talked to the KE Station manager, a very nice guy, at the gate--I decided to stay in the lounge for 4+ hours, slept a bit... then it was time for departure! After talking to him, here is the deal:
1) Still not sure if they officially sell F on this route.
2) When Y and J are full/oversold, they will put pax in Rows 1-2.
3) When not 100%, they curtain it off, turn out the lights, and nobody sits there This is what happened to me, since J was less than half full on my flight last weekend. And, something else: NEVER sit in Row 10 of J class on a 773! It's got at least 3 inches less recline than the other rows. Luckily, there were plenty of open seats, so I moved to 7D, and it was actually decent. I'd sit in Row 7 again for sure.
4) If they sell even one seat in F, I'd imagine it's even harder to get up to Rows 1-2.
As for getting that seat when they are using a "Premium J" cabin, meaning they're using the Old F for J pax and providing J service to them:
Based on my experience on the ICN-ORD route, IF they do open Old F for J pax, I think it's quite difficult to get seats anyway, unless you're KE Morning Calm Elite, since I got an onboard upgrade to seat 2J on the Old 744 to ORD (see how I did that here:
http://www.flyertalk.com/forum/showthread.php?t=841928
Talk about lucky--one, that I asked the right FA, and two, that they hadn't filled Rows 1-4 already!
But FYI: Even though I was on a paid C Class (albeit a DL codeshare) ticket AND am SkyTeam Elite Plus, I was not automatically placed in Rows 1-4 on that flight. I highly doubt all the other 14 pax in the Old F knew to ask ahead of time! Somebody put them there, but who knows who did it--and why?
Though I did get my first BP in BKK from a TG staffer at the KE transit desk--I also checked with KE Lounge staff, and wasn't moved to Rows 1-4 by them either, meaning seeing my BP and looking at my booking (and seating assignment) didn't ring any bells for them.
At that time, I didn't realize that was the configuration being used until I boarded. Had I known ahead of time and asked, even then I'm not sure I could have gotten it. You're pretty much stonewalled 100% of the time when asking for these seats if you're not Morning Calm Elite.
But doing your homework ahead of time will definitely help you--that is, IF they are willing to do it.