Someone please let me know? Did Kirby work within the Marvel offices in their much proclaimed 'Bullpen" era? or did he work from home or a personal office space? This is going to be a key determinant. I hate to say it, I have looked at the Kirby case a lot, and I have to say while Kirby in hindsight probably deserves more and more credit than he got, I still do not think that there is any legal basis to challenge the status quo. At least none that will succeed.
Kirby was the artist, but he was part of the collaborative Bullpen environment. Office space and facilities were provided by the employer. He was work for hire. A temp if you will by todays nomenclature.
Jack Kirby was pretty much the case study for "starving artist". He was a brilliant artist with an eye and hand and use of colors we had never ever seen before. He was also a piss poor business man. A simmering bundle of grudges that to all appearances never had the ability to properly assess the value of his own work, market it, or capitalize properly on his own fame. Case in point his DC Fourth World stuff. After he felt screwed by Marvel, he then, as the industries rock star artist, moved to DC. Did he negotiate a hugely lucrative contract? Nope. He did some self created stuff as well. How many here know what books or characters those are? Be honest.
Stan Lee was in many ways the best thing that ever happened to Kirby. Stan Lee out PT Barnums PT Barnum. He is perhaps the worlds greatest marketing guy. Consumers should be thanking the gods that he found his calling in Comics rather than selling us something like Cigarettes or Beer. It was the marketing push, the ability to sell the art that gave value to the art. The words as much as the pictures. And quite frankly Lee is or was a better businessman than Kirby. It sucks. Especially from Kirby's point of view. But how much is it the courts role to protect one from oneself and ones ability to make informed and coherent business decisions?
Have both the public's and the comic companies opinions changed regarding creator rights in modern times? Yes, most certainly. And part of that is the industry has evolved and grown from 5 cent funny books for kids on the rack in the drug store to a billion dollar industry. The law evolved over time as well. But a key legal principal is that law is not retro active. 1960's copyright law would still be the authoritative body for anything involving Kirby and Marvel, would it not? (and as far as that "new" 1970's contract that Marvel offered Kirby. No that is not an admission of anything claimed by the plaintiffs. The fact that apparent major changes to copyright law were already in the pipeline heading to Congress is just as much a legitimate justification for that new contract as any ulterior motive. Marvel's lawyers would have been negligent to not know what was coming legally and start creating contracts to reflect it.)
Kirby's family probably has a legitimate case to withdraw the rights to any actual Jack Kirby created art. They could block Marvel or seek payment for any use or reproduction of Kirby's actual drawings. That is his body of work. His and only his drawings of Mr. Fantastic, the Thing, etc. Not the characters. Not the character designs. Just his actual line work.