Ah, a topic near and dear to my heart. Keeping in mind that I'm not a lawyer, and that although I do freelance work for Hasbro and Fun Publications, I cannot and do not officially represent either organization, here are some of my thoughts on the matter. I will only be referencing publicly-available information.
The first factor is exactly what Zac wrote so succinctly above.
Rights are complicated.
Lawyers are expensive.
If there is doubt exactly how much of a property you own, even if it's only a little doubt or you're likely to win, most companies would rather avoid the issue than have to deal with the legal issues, again even if they have a great case. It's just really not worth the hassle and money even if you are in the right most times.
Transformers has a 30+ year history with plenty of iconic characters and ideas to draw from. There is little reason for anyone to focus on the few bits Hasbro owns that may spark a lawsuit. The nonsense with the Transformers/G.I. Joe Skystriker lawsuit, despite Hasbro winning the case with prejudice, pretty much consigns the Jetfire design or anything close to the dustbins of history.
There's another, equally important factor. Bandai, a minor Hasbro and major Takara-Tomy competitor, unquestionably and unambiguously owns the rights the MachineRobo molds. Hasbro is not in the business of giving free advertising to its competitors. Thus, whatever the rights situation with the Challenge designs, Hasbro would have a strong disincentive to using them.
Now, what is the actual rights situation? It's very difficult for anyone who isn't a lawyer directly connected to the 30-year-old contracts to know with absolute certainty, however we layfolks can make educated guesses. Here's a copyright notice from a 1984 GoBots picturebook:
There are a couple of interesting bits here. One is that not only are the names used under license from Tonka, with no mention of Hanna Barbera, but the character designs are as well. Two is that it's not only toys that are used, but characters and concepts specifically from Challenge. All of the major human companions as well as the element sorium are specifically name-checked. It would appear very likely that, whatever contracts Tonka and Hanna Barbera signed, Tonka kept the majority of the rights. Note that the Challenge episodes themselves contain similar notice, giving full rights to Tonka. However, 1984 was a long time ago. Might something have changed in the interim?
Fast forward to 2011. Warner Bros Animation wants to release Challenge on DVD. For the first time in decades, someone with access to (one presumes) the original contracts is in a position to want to pay lawyers to untangle some of the mess and see who owns what. The result is thus: http://tfwiki.net/me...tice_modern.jpg
Which says: "GOBOTS and all related characters and elements are trademarks of and © Hasbro Inc. Program Compilation © Hanna-Barbera and Hasbro Inc. Package Design © Hanna-Barbera and Warner Bros. Entertainment Inc."
Thus, it seems very likely that, at least as far as Warner Bros. is concerned, Hasbro owns the characters and elements, and probably the designs as well. And so, as of 2011, were Hasbro so inclined, they could mine such elements. Yes, even the designs...
...but they won't. At least, they wouldn't use anything too close to any of the actual GoBots characters that were based on a Bandai license, because again, they'd not want to boost Bandai's MachineRobo line. A Cy-Kill toy that looks like Cy-Kill is probably off the table forever (pending some fortuitous merger). On the other hand, a Cy-Kill with a different color scheme and silhouette would be entirely possible. See, in fact, the actual Cop-Tur and Bug Bite toys produced by Hasbro licensee Fun Publications. A non-toy Cy-Kill would STILL almost certainly need to be heavily redesigned, not because of a potential lawsuit, but because of the free advertising issue.
I suspect that, the closest Hasbro would be likely to allow for anything too related to the old designs would be some kind of non-visual medium. Visuals MIGHT be possible for things that have no Bandai connection, like maybe some of the human characters or toys like Zod which were produced entirely by Tonka with no Bandai input. But for someone like Cy-Kill or Scooter, they'd have to be either entirely redesigned or shown in a completely obscured way.
But, again, this is all speculation. Only the Hasbro, Warner Bros., and Bandai legal departments know for sure.
Edited by Jim S, 22 February 2016 - 06:42 AM.