EK availability gets very frustrating when it is down to the last few seats. For the next few days, flights PVG-DXB and DXB-LON are very full.
Further confusing the issue will be the way EK deals with 'married segment availability' - a complicated tool that is a way of assigning more or less inventory on flight B based on where you came from on connecting flight A, or vice versa. It has the effect of making searches for availability much harder, because availability for travel PVG-DXB and DXB-LON does not imply that the seat is available PVG-DXB-LON.
The odd few full fare Y seats you are catching glimpses of are the most expensive economy bucket available. Fare difference between QEJLPGB1 and YEE1YGB1 is ~GBP500 one way (depending when you bought it) plus a change fee of GBP75.
My advice is to spend GBP497 on the direct Virgin 251 to LHR tomorrow morning. It's cheaper...