She will play the future, unseen incarnation of Greta Gerwig, the show’s female Ted. Whether or not Greta Gerwig will spend the first two seasons of the show bitching about how she can’t find a husband the same way Ted did about a wife is currently unclear, but probably.
So, that’s that. Meg Ryan will be the voice of the mother, destined to capture audiences with a tale of love, only to piss them off with a finale that stabs all the loyal viewers in the heart.
It should be pretty cool.