Yes, it probably won't surprise you to learn your lamentation is a common one. Probably the single most common request in the history of the game. As a result we're now testing a system to expand your household to contain as many as 80 people, however the code was written originally for a game with two slave slots, one you were training and another as a helper/favorite, like Slavemakerr3. He's re-writing the code from the ground up and the new system is expected to go public the first few months of next year.
In the meantime you can get 9 extra slots from the Retreat and marrying one opens up as slot as does sending a girl to the Arena so you can have up to 19 currently.
I understood that the proposed changes (8.3) would be seen at the end of the year or the first days of next year. Am I wrong?