A new mythic path seems on par with the effort of adding turn based mode to kingmaker.
I was responding specifically to this statement.
That said, I also think any significant fleshing out of a mythic path would be more more expensive than adding in turn based mode, simply by virtue of the fact that it would require more people working on it. You might be able to just add in a few extra phrases or abilities easily, but new story paths or story would have all the same problems as adding in a new full path.
You've nailed it pretty well there, I don't have much to add.