Originally Posted by BenKenobi
Kang was actually the one that got me thinking. Vulcan I can't see being split since his creation came about after the X-Men deal.
Marvel we know has the rights to the Kree and the Skrulls (The Kree coming into Guardians and the Skrulls originally to be used in Avengers but scrapped so they could be "saved for a bigger project"). Kang is really iffy, yes the character appeared in the Fantastic Four, but he's much more an Avengers villain and Rama-Tut was an old identity. The only thing he really has linking him to them is his lineage. Anyway if Fox doesn't have the rights to the Kree, the Skrulls, or Kang I really don't see how they could hope to establish a universe for them. The Fan Four are great but they're also some of the most misswritten characters in the Marvel Universe.
Also some others I thought of:
Hydro-Man (Spider-Man/Frightful Four)
The Beetle/Mach V (given the character was largely a marvel wide misc. foe until the foundation of the thunderbolts.)
Vulcan actually ticks all the same boxes as Quicksilver and Scarlet Witch. He's related to famous X-Men, and he's a mutant. However, many of his stories (including his crowning story, War of Kings) were told outside of the X-universe.
Sony probably has the rights to Hydro-Man just like they had the rights to Sandman (who also fought the F4.)
Beetle is probably a split rights case, though neither company has a huge incentive to use him right now.