That's exactly it hahaha sorry for the delay in replying
I am open to adding new fetishes and I considered SPH as a separate fetish skill however the issue I faced was that there needs to be some visible progression between the fetish levels and for SPH I struggled to come up with more than: do humiliation (there could be some variation in intensity). That said it is not a closed topic (I am also a fan of SPH)
These are very good ideas... Might make it part of some session ;).
From personal experience I see no issue with SPH in a romantic relationship if both parties enjoy it. There will definitely be SPH in the game (already is and more is coming in the upcoming upades) but it is part of cuckold fetish because more extreme SPH will involve some third party. If you have cuckold fetish high enough (only level 2 possible right now as it is tied with the plotline, but more coming in the future), there will be SPH also chastity and prostate play plotlines as well as other sessions.