McDonnell F-4M(FV)S Phantom II High Variable Sweep Wing Fighter

American planned McDonnell F-4M(FV)S Phantom II High Variable Sweep Wing fighter jet variant pic.twitter.com/Ff9P9JHXH7

— Caesar (@Ninja998998) November 27, 2019

This plane looks to me like it would have been a MONSTER (assuming it had the right engines to push it along). 

Having said that I really hope the USAF is successful in its push to go back to the "Century Fighters" type development in this modern day.  That would give all the new designs (and improved variants) a chance to at least see the light of day.

To my knowledge the F-4M(FV)S was never built.  Not even a demonstrator.  If it had it would probably have gone the same way as the XF8U-3 Super Crusader, another MONSTER of a plane that didn't get into service.

Are there these kinds of mods floating in the mind of an engineer for the Super Hornet, F-15 etc...?

I bet there is.  Hopefully with the return to past development cycles we'll at least see them on paper.