Good luck with the family stuff!
Anyways, I was thinking, how about a challenge that we complete to use the Spellbook and Spells? You have to, anyways. It breaks the rule, since you can Summon Sims to your lot, and interact with them. This can be another Challenge that is only required if you have the spellbook, because it wouldn't affect anything else!
Also, when Pets comes out, how about a Challenge that restricts using the "Unleash Animales" spell on other Sims, since the spell makes them act like an animal. Again, this wouldn't affect anything since it would only apply if you have the Spellbook! (This doesn't mean I'm okay with the Spellbook they gave us. I still believe that they should give us REAL magic.)
I added a Skill Activity page to the Restrictions Category. I'm filling it out as I go. It doesn't appear under the main Restriction drop menu, but I guess that's because you didn't make it, mikitta.
AS written, the Build A City challenge dosn't play well, so it really wouldn't mesh.