Does anyone else out there think that Future Foundation Doom will convert into G.E. Doom at a particular click on the G.E. Doom dial like how Hellfire Club Jean Grey converts into the Dark Phoenix?

If they had come out in the same set I think that would have happened. I don't think they'll have a new piece convert into an old chase. It'd be cool though

You never know. The 2017 convention exclusive Plastic Man interacted with only the JW one at the time.

They added Shifting Focus versions of Superman and Batman after the fact, in Elseworlds.

Or the Hulked out Hero chases who reverted to specific characters from other sets.

ConEx Apocalypse transformed into GSX.

I think Wolverage, a chase in The Hulk set, reverted to 2 or 3 other Wolverines from other sets.

You're right, Wolverage did. I believe the options for him to revert to was the Chaos War uncommon Wolverine, the GSX common Wolverine and the FF GSX Wolverine.

There is also Bruce Banner from Incredible Hulk set who could transform into various Hulks from the IH and GG sets. They did similarly with Rick Jones.

They also did it for Matt Murdock for him to transform into various Daredevils.

Before Shifting Focus, there were all the Ant-Man pieces with a similar concept that worked with older Ant-Mans too I believe.