Looking at EF you are right, both the VS7 and VS23 outbound and VS8 and VS24 inbound have light loads that day, however both the VS8 and VS24 are fullish in Premium and if the seat map feature on EF is any guide both look like less than 50% full at the moment. Worrying [:?]. That said, it is still more than six weeks away and things could change and more bookings come in.
EF is however confused - it shows that on the following three days only the VS7 is running but still shows the VS8 and VS24 returning - I'm wondering if VS have merged / are watching this and only booking on the VS7 to make a final decision ... but then on the VS Web site a dummy booking shows the VS7 and VS23 operating on the 27th but only has availability on the VS8 returning. Whereas they are still accepting bookings for your date on both flights. Strange and confusing [?] but all adds up to the likelihood of flights merging on some of these dates but potentially not yours ... perhaps a staffer might help here?
If you are booked Gs and they do merge VS should reprotect you in Upper if you are moved to the VS7 however. S is in Premium, not sure if that's what you meant but guess you booked Premium and upgraded with miles?
Rambling reply [:w].
There's a plane at JFK, to fly you back from far away
all those dark and frantic transatlantic miles