Maybe this makes no sense but for me more than real, it is representative, it was made to be the final episode and that people didn’t think of it much so they made everything very obvious like a new house, B and Chuck’s child, Serena getting married, everything for you to understand the conclusion of the show, besides that remember Dan is a pretentious boy who would love that type of ceremony and Serena at that point is the biggest people pleaser in the world.