Ranai's blog has an interesting discussion of the German BDSM film Verfolgt (meaning "Hounded" in German), released as Punish Me in English. (IMDB) Briefly, a young male criminal and his older female probation officer begin a sadomasochistic relationship, with her on top. (I haven't seen it so I can't discuss the film itself in detail.)
There's a lot of food for thought here, about the nature of male submission and female submission, its depiction in media (both mainstream and pornographic), and the influence of the commercial BDSM scene on the non-commercial. Fashion choices are only the most obvious form of this influence.
Elsa doesn’t need a costume. Inside subcultures, dictates of commercialisation and sexism still cause a good deal of female hetero beginners to ask ‘I want to dominate my man for the first time. What should I wear?’. This does not refer to people who actually have clothing fetishes themselves, but to people being collectively or individually pressured into costumes. It is immensely pleasant to see a female character simply going right ahead. Costume? What costume?
Jan and Elsa don’t buy and sell their interaction. They are in a personal relationship. Most people don’t get told by pervasive cultural narratives that the default of their sexuality is sex work. Heterosexual dominant women and submissive men get told just that. Our culture still overwhelmingly frames a man submitting to a woman as a commercial service which a man buys from a woman he is not otherwise in a relationship with. To the point of casting dominant and sadistic women as sex workers by default, and submissive and masochistic men as clients by default. To the point of pressuring many women into imitating prodoms and porn performers in their personal lives, and to the point of causing many men to act as if they were clients even in non-commercial, personal contexts (client mentality). To the point of, in the wider culture and in many sadomasochistic subcultures, effectively erasing and repelling women who happen to be sadistic and/or dominant in their personal lives. It is gloriously refreshing to see a story of a submissive man and a dominant woman doing their own sadomasochistic stuff inside a personal relationship.
A malesub-femdom love story would be so against the grain of culture's rules about love, sexuality and gender that it might be illegible as a love story. People would look at it and scratch their heads, unable to understand it.