I myself don't mind the grind, and if you want to speed up a few fetisihes you can go into the sim room and grind a girl. But I can see getting a fetish weakness so exp gain is faster, and a fetish blocker so a fetish develops even slower. A way this could work would be something like holding the holy thighble, so anal vaginal and oral develop slowly, but thighs would skyrocket. Or a book on Monster Breeding, which would make it to where Furry, Scaily, and Robot give less exp, but Monster and impregnating go up.
This might be a pain to program and balance, so definitively up to Finchy.
(PS, Finchy has said that since there is a lot of demand for Romancing/being owned by the girls, it is a real possibility in a future update to do something with the free wife. I myself am looking forward to it, but I understand letting him cook. Maybe it will be in 6-9 updates, only Finchy knows.)