I can confirm that ever 744 I have flown on with VS
has this. thats G-VROM, G-VLIP, G-VROS, G-VHOT, Ruby Tuesday and Lady Penelope.
I asked this question a while ago about the A340-600 having the same thing in row 19. I got the seat once, and was very disapointed!! There is just a blanked panel next to the seat. The conclusion that someone came up with was that this was a fusilage joint.
Another theory was that it was there in case an engine blade snapped off...and the third response was the air con duct.
I havent heard a confirmed answer yet...other than I know for a fact its not a galley, toilet or rest area access...