You found your way to the magic!
As long as my wife is assured that we are only fantasizing and there's no risk of facing all the fallout she will talk about having bigger cocks and doing things she normally wouldn't. I see it as a seed. Just having those thoughts in her head is a victory for me. She has gotten much more descriptive with her "dirty talk" in bed. I asked her to help me stay aroused so she's coming up with her ideas based on what she thinks will get me excited. When you're dealing with a sexually reluctant spouse the small steps appear to be the most foundational.
Yes, exactly. Every small step is a little victory. It really can't be rushed. Push too hard and you might find yourself taking a step or two backward, or worse, having her shut down the idea completely. It comes down to them changing their whole belief system around the idea.
Let's face it, our society's belief system =
+ monogamy good, nonmonogamy BAD;
+ sex with anyone other than your husband, even with his consent, is cheating and BAD
+ sex with multiple guys, SHAMEFUL
+ enjoying sex with others outside your marriage, SHAMEFUL, not to mention humiliating if anyone were to find out
+ a husband who enjoys his wife infidelities, embarrassing, not to mention an unloving husband
...just to name a few
It's a lot to work through. One by one they need to take each of those beliefs and when they come to the realization they don't hold water, are no longer useful, do more harm than good in most relationships, and without those beliefs, they can have an incredible sex life, with a devoted husband, and a strong marriage, well, that's when the tide turns and the adventure begins.