If you two are in love and respect each other, the only threat you can make with an ultimatum is the threat of leaving. 

The unspoken words behind these are:

"I love you less than <goal>, and I don't trust in your leadership to get <goal>".

If you loved him more, you would not threaten leaving him, and if you trusted him to lead you to this goal, you would instead simply tell him your goal and wait for his leadership. After the ultimatum, things will get shaky, even if your love agrees to your condition.

He now has to find something to love more than you, so that he is not Priority #2 for you, while you are Priority #1 for him. If the goal that he finds isn't the same as yours, you two will have different goals. You are no longer a team and can break up at any point to reach your separate goals without each other. If a relationship does not have the same goals, it cannot survive difficulty.

The only way it can survive is if your partner has the same goal. But this is not the same thing as agreeing to an ultimatum condition. That is just appeasing you while looking for a goal.

Moreover, you are a woman and when he agrees to your condition, it means you now have to be the Captain and have to be the leader, planner, and fixer. Because you are the only one among the two of you who understood the importance of the goal in the first place. So you have to carry the relationship on your shoulders and assume long term Captain responsibilities of achieving the goal, managing resources, checking in with everyone's happiness and morale, and taking responsibility for any failures and setbacks.

This limits the feminine strategies you can use in the future for this goal, and perhaps others.

It rules out vulnerability. You can no longer be vulnerable or inspire him on this issue, as he is already aware that you do not respect his leadership and prefer your own. Most red pill feminine tactics are no longer applicable, especially submission. It also rules out "bring him your problem, not your solution". 

By making an ultimatum, you abandon your feminine RPW powers and step into a masculine role.