Well... I'm not going to argue that that's a great possible way to explain where Red Skull went that also goes along with Cabe and many other connections in different ways that are tough to explain...
If some sort of PlanetHulk/WWH scenario happens my source has told me it's more like he's being framed by Sterns and a clone of Thor comes into it... as well as possibly Bill a little later.
There might also be a way that Sterns connects Red Skull and Red Hulk eventually, and as I've been describing to Jaqua over PM's earlier this leads to more of a Hulk being framed scenario during CA3 as they're trying to create clones and shall we say Dark Avengers that would come into the planet Hulk and WWH elements. Part of the masters' plans may be to eliminate some of the heavy hitters before they start to strike. this might mean manipulating events to get Hulk kicked off the planet. Essentially, we could eventually see some of the masters trying to frame and create their own Avengers from that sample Tony has at his tower that Loki stabbed Thor with, once Sterns is free from prison and joins the returning Masters.
The thing about the early concepts for Leader is that he's not always presenting himself as a monster even though he looks like a green goblin now.... Once sterns is freed from prison he would pretend to be good for a while by actually helping the Avengers and Banner in a big way against Thanos... as part of his deal for getting out... he feels wrongfully imprisoned. And a storyline where Leader creates Hulklings and Thorlings for the masters in CA3 and some of it transferring over to Avengers 3 could be what's used to set up Planet Hulk and elements of WWH in Avengers 3.... Cap 3 would be more of a team movie and ALL the other Avengers (including War machine and Black panther...) besides IM, Thor, and Hulk will be in that movie helping Cap defeat Zemo, Skull and the masters. if Avengers 3 is WWH elements and Ultron.
Sif may even join the cast of that Cap 3 concept and deal with Enchantress... Part of it would be set in Wakanda... Most of the masters are defeated by this team. Enchantress, Sterns and Ultron are the ones to move to Avengers 3 and relaunch a plan. But Ultron has plans of his own. First he needs Sterns to clone Thor from that sample and make it look as though Hulk just killed Thor...
Some of the Avengers buy into this... most and Cap don't. Remember the team will be a lot bigger by this point.
He met the true Sterns that is just as monstrous as his appearance in Cap 3. CA3 occurs when all the other main 4 were busy...
Thor hasn't even returned from dealing with Surtur when Hulk is set up...
Tony is off in space after Avengers 2 and his extremely brief guardians cameo. Now he's with the guardians during the time of Avengers 3...
So Leader is kind of playing all sides after he gets out of prison, including possibly Hammer in CA3 and a returning Mandarin... But Rhodey would have to deal with Mandi this time... and possibly some of the Hulk clones/The general becoming Red Hulk.
Part of the reason his appearance turns red is the same reason abomination is Red, the same reason Hulk's blood can be a problem, and Thor's takes a little longer to figure out. The serum is within Hulk's blood. And Sterns wants to make his own teams.
Wants to take the world for himself in the absence of Hulk, and most of the masters are killed in Cap 3... Sterns wants to be the Leader of the Masters of Evil... but Ultron will come out on top...
Sterns is more like our Osborn character... he'll do a little setting up of Dark Avengers elements that are already being put in place to be mixed with the WWH elements. Whichever IM villain is coming back bring him that Iron Patriot suit for his teams... Convinces the world he is good and Hulk is bad, despite the way things appear before because of how he goes about playing all sides.
But more like trying to turn people into hulklings like in one comic story. And then later Thorlings and Caplings for Ultron...
To get someone else to turn into a version of Hulk is very hard for him to do, they keep turning Red like Skull and Abomination and Red Hulk.... He needs a little bit of that original super soldier serum combo that created cap. When he applies what he got from Abomination and himself in his transformation to the general it gave him Red Hulk... and that was no good for framing Hulk... He had to clone Thor and make it seem like hulk killed him to neutralize Hulk for Ultron.
Red Skull would be gone by this time, but him and Zemo form a big part of CA3, along with other villains... They had already found Red Skull before this and knew exactly where to send Hulk during CA3.
The money the Baron provides allows for Sterns to continue Hydra's work, and make it seem Hulk is the villain. and Cap leading another team of Avengers versus the masters. Sterns is part of this but left with the power. Ultron is not really a master, only he would rule this empire they've been trying to set up. When he gets a body again after the origin movie he does
I have no worries that we'll see a lot of villains return in CA3 or Avengers 3. But I think only Sterns, Ultron and Enchantress make it into Avengers 3 now... if Szostak is Cabe.