Actually, there is. When having non bondage sex with the girls, they will gain 1 point of 'disposition' towards a sex act (penetration-wise) which will make her cum. Anal orgasm = +1 anal; orgasm when sucking cock = +1 to Oral and +1 to Oral Fixation (whatever that means)....
Sadly, having GIGACOCK makes it impossible to have "request sex" session with a "too few points" slave. The only option is sex during bondage session, and I have yet to see any increase of proclivity toward that type of sex from it. So... unless I'm missing something, bigdong-blocked?
Basically, right now mongodick seems like a noob trap.
How does that relate to the problem of eternally having too few slave slots? Still, that would be neat indeed...
I assume there's a limited number of slave slots for that reason - so the potential for repetition is limited. Don't get me wrong - I like games that give options for playing how you like, but sometimes it might detrimental to the overall experience.
Lab Rats 2 does something like that with procgen combination of body type, skin color, faces, hair styles/colors, and the like, and the effects are... serviceable, but often rather off-putting. Could be just choice of pre-rendered faces, though.
The "unmentionable" Free Cities mod also has some (Daz, I think) renders with similar customizability lately. That ones are actually pretty nifty.
Personally, though, I found that as soon as I hit double-digit number of slaves in Free Cities they slowly lose their uniqueness and memorability, so the individual approach of MoR might work much better in that respect.
On an unrelated note, apparently the game wants me to play with SchizoJune: