The ability to talk to RomanceKas about God Offers for my Soul, and having her counter offer with Semi-Perma DragonTF.
She would (and should, imo) be the only source of DragonTF, and doing this would make RomancePath as rewarding as taking a Soul offer.
Aleih could even help teach how to breath fire, and it would be wholesome.
Now. frankly, as someone who wants the dragon tf but does not want to romance Kas (for many reasons), I would like to veto this.
First, while kas and her daughters do have dragonic traits, they did come artificially so locking it behind her seems kind of a strech. Sure, there are many ways you can justify it (she is only one with ability to do so for example) it would still feel like a strech to me.
Second, dont you Kas lovers already gain new sex scenes, events and different story route by just dating her? That is way more then any of the current soul bound content adds.
Thirdly, and slightly tying to second point, the way you worded your first sentence comes of kind of manipulative. "Oh Kas, my love, these so called "Gods" are tempting me with the promises of riches and fame if I just sell my soul to them to become their champion... N-not that I am considering or anything, but, I am just saying, if you happen to have anything back in that fat trunk of yours to make our love for each other all that more unbreakable, I would not be opposed to it..."