Well I think they should go with a system of sliders and traits that complements each other.
For example slob to neat could return like it was in sims 1 and 2. That's a good slider. But Squeamish could still be a trait that can be added to this, available only from a certain neatness level since it would conflict with being a slob.
I think when you have a shy/outgoing slider and a gender preference slider that ranges from 100% interest in men to 100% interest in women, there could be several romantic focused traits that interact with that and some could require a sim to be either more shy or outgoing.
Like not having romantic interest in any sim could be a trait.
Flirty sims would want more romance, and how much they want to woohoo could rely on the shy/outgoing slider. The shyest sims can't be flirty, but from say, 4 out of 10 points in this slider a sim could be flirty. A fully outgoing sim would constantly want to woohoo.
