Babies are enough of an incentive to complete a breeding IMO. I'm pretty sure plenty of users would complete breedings even if they didn't make back the KS from it. Whether they'd be happy with the change is, of course, a completely different story, but in the theoretical situation that this was the only option, I'm sure people would still breed. And given that the point of the change is to cut down on breedings, if folks don't breed as much as they used to, then that goal will have been accomplished.
If we reduced slots to two per person, but made rooms one slot each, then people could either do two self-breedings or FOUR shared breedings, which... is more than our current system allows for. With three slots and rooms being two slots each, you could only do one self and one shared, or three shared in a month. Again, the goal is to reduce litters so mod focus can shift to other areas of the site. We're not trying to abandon the breeding area, it just shouldn't take up as much time and effort as it is right now.
As for the idea of those who RP more being able to breed more, that's basically what would happen if the KS gains in the breeding area went away. You'd have to RP more elsewhere in order to breed more. Raising KS costs of rooms would do the same thing--- you couldn't just RP in the breeding area, make up the cost of the room, and breed again.
And to belatedly address the slots issue--- I only proposed that idea as an alternative to paying out KS for unused slots, because that felt like an even more easily-exploited idea to me. If it were implemented, then yeah, the slots would have to have limitations put on them like the ones Atoli suggested.
I initially had my reservations going into this, but the more I read of this discussion, the more I'm starting to prefer the removal-of-KS-gains idea.