10 days ago I was on ORD-LHR in PE (787), and about an hour and a half before boarding (enjoying the Flagship Lounge relax room), I got notification on the phone of a new seat assignment. Checked at the desk and had been given an op-up to J due to PE being oversold.

If you are an EXP and there are any J seats showing open with you being in PE, you may end up with an op-up. Personally, I liked getting a freebee for the long haul as I usually have to use miles/copay (SWUs were used earlier in the year for personal vacation with wife). Maybe this will keep happening as I have 3 more long-hauls on this leg in the next 4 months - all booked in PE, and all looking full except in J.