Well, i just finished the game and i loved it, but i would love it if there were more option to pursue consensual BDSM relationship with those slaves that get corresponding traits, up to the point where SM actions actually regenerate their status. Another thing i would love is to get more options for SM play, but not offered on the plate, but having to unlock them by means of buying corresponding equipment, which would be scattered all over the world in cities, i love exploring and unlocking new things, that is what keeps my interest, maybe some of that stuff could even be acquired trough a sidequest. 

Some suggestions i would make for the devices are hypodermic needles, breast press (the kind they used to use in vintage BDSM clips, with two screws on each side) a simple ball gag, (as opposed to ring gag, to muffle the slave), pin wheel, alligator clips (more painful then regular clips), anal beads, some sort of magic shock prod(could be a whole range of magic shock devices really), and speculum.

Some less conventional and somewhat more extreme stuff you may want to implement (if you want your game to go that way) could be canes(more painful then regular whips and unlock foot caning, that is even more painful), throwing darts(blowgun?) nail boards (that slave would be forced to sit on or be pressed against), pears of anguish (may or may not be harmful depending on how you want to implement them, modern versions only extend a little bit, but proper one was designed to seriously harm, so you may or may not implement the system in which you can cause serious harm to a slave if you expand this too much), pliers (for squeezing sensitive body parts) and longer thicker needles(perhaps even spikes). 

So far as i can tell all this stuff in the second section would up the ante of the SM acts that are available currently, so you may well not want to go there, i just wanted to provide as many options as i could dig out of my memory, thanks for your attention.