Dan Fogelman offered no huge reveals regarding what This Is Us has in store for its ending, although he did tease (via Deadline) a Season 3 plotline does play into the show’s end in a way.
It’s best not to speculate when it comes to This Is Us, considering Fogelman has a way of making an audience think one thing is happening when it’s really going to be another.
Does the “her” Randall and adult Tess refer to in that scene play into the show’s finale?
The show creator said Randall’s flashforward at the end of Season 2 is in some way connected to the show’s end overall, which certainly magnifies the mystery presented in that scene.