The GMA video aired in Nov of '86 (probably shot a week or two earlier perhaps). The earliest blueprints I've seen of the stage 9 TNG layout is March of 87. So it's likely the red carpet was there just for that shoot as not much had been designed or planned for TNG at that point.If this was late 1986, perhaps the carpet was for early test shots of TNG?
There was another set-tour from that time period on a Showbiz Tonight-type show with James Doohan leading a host through the sets. It was up on youtube a while back, can't seem to find it now -- might have been aired on just a local station, but it was the same kind of set up. The host and Doohan were talking in the entry foyer to engineering..