In the novel Pride and Prejudice the concept of upward mobility is evident in the love matches of Elizabeth and Jane to Darcy and Mr. Bingley, respectively.
Although both sisters belong to a respectable family they are by no means aristocrats nor, for that matter, "fashionable" enough to be found mingling in elite social circles like Darcy's or Bingley's.
In fact, Darcy went as far as admitting that he felt that the distance in social ranking between himself and Elizabeth (as well as Bingley and Jane) was big enough for him to consider his proposal to Elizabeth a form of self-sacrifice.
Later in the story we witness a change in Darcy's views of pride and prejudice and the story ends with both couples reunited.
We also know that the lives of Elizabeth and Jane certainly improved thanks to the joys and comforts that are often associated with rich households.
Therefore, upward social mobility is possible as long as the person of rank who chooses to marry a person of lower birth is content with knowing that there will be no dowry, no fusion of family estates, and no increase in the family fortune.
That would have been a rare thing for any rich and prestigious family to accept, so it was not the norm. In any case, the benefit remains entirely on the person of lower birth who will basically be living a dream come true.
I just want to add an interesting note: it turns out that Bingley's ancestors made their fortune from "trade." You'll notice Caroline smirking about Elizabeth's uncle being an attorney in Cheapside. Well, an attorney is in "trade" as well--he belongs to the same social class as a merchant who might get lucky and strike it rich.
It's pleasing for the reader to discover Caroline's hypocrisy, although you will only discover it by reading the novel closely. It also shows that upward social mobility is possible, since no one seems aware of or concerned about the origin of Bingley's fortune.