As for legal hassles, I've discussed this with my Attorneys, and even more to the point, my youngest daughter who, in a different life was a Legal Secretary in a law firm dedicated to Contract Law, and was deeply involved in Model/ Property Releases, Advertising Contracts ... etc. The stories she can tell (especially, why the release was shot down in court) could curl your hair.
Her one comment: "For the most part, the `boilerplate releases' found in the Everything You Need to Know as a Photographer books are worth much less than the paper they are printed on ... and the most common fault: Too broad. Specificity is important here."
(note 1) I'm not done, yet. I haven't asked the models directly about their perception of "co-ownership" of images. I'll grind that fine... to be more confident of my impression.
BTW ... You did kind of "throw" me here ... where the "someone who posed came back and sued the photographer (or in the worst case the estate of the .... Model...)" Model? Wouldn't the person who posed be the "model"?
They would be suing their own estate????