There was really never any hope of seeing Filmation characters in MOTUC.
Keep in mind that, according to Mattel, to produce these figures Mattel would have to purchase the entire Filmation archive from Classic Media. That includes lots of animated series. Why would Mattel ever go through that sort of investment to produce a handful of action figures? Mattel have no interest in promoting these cartoons, and no means of doing so even if they could.
To get Filmation characters in Classics we would need a policy change that would allow Mattel to purchase on a few characters, such as those from the MOTU and PoP cartoons.