Maybe Lynch is trying to tell us something about the town of Twin Peaks in 17 and everyone missing in 18? But not that Twin Peaks was just a dream and that we get an actual conclusion in 18 in my opinion.

Instead of Twin Peaks being a dream in 17 may be Lynch is telling us he is completely done with the town and most of it's characters going forward. They will disappear but not because they didn't happen. During Season 3 most of the characters seemed to get little time and that amounting to fan service really. It's seems clear watching Season 3 that Lynch had little interest in going back there. Episode 17's end plays out a lot like a goodbye to Twin Peaks and it's characters. 

Episode 18 has none of Twin Peaks as a town. The only characters that show up are those in the Red Room. While watching it we get more new locations and when we go back to it there is little of what we know as Twin Peaks there. A couple of locations and when we see the people in one of those, the Palmer House, the Palmer history is not there. Most of the episode deal with characters, Diane and Cooper, who are not from Twin Peaks. Maybe we are being shown the show as it may be if it goes on. The episode ends with a shot of the only 2 characters I think Lynch wants us to know are essential to the series, Cooper and Laura.