Sir Swindle:
Super powered and scientifically plausible are sort of a weird combination right? A five story tall dragon can't fly scientifically but if it has super speed and strength powered wings then who knows right?
Post apocalypse thing is interesting but you are right, it might make a better straight post-superhero-apocalypse setting. It all depends on how fantastic you want your fantasy. Calling out that 'this is earth year 3042 after the aliens took all our copper and silicon' sets a different tone than 'this is the world of Avalon where the land is ruled by the immortal king of light and the countryside is plagued by servants of the dragon beyond the mountain'.
I saw Fantasy and I imagined the second one (straight high fantasy) but i would app to either.
Look at the world of Tekumel as a good example of how this might work. That milieu is based on a far future relapsed into barbarism after an apocalyptic event which isolates Tekumel and its sun and sister planets from the rest of the universe. Magic is essentially other-planar force which can be controlled by the technology of the Ancients or by more purely "magickal" means.
The Gawds of Tekumel are other-planar beings whose presence in the world is demonstrable and frequently felt.
Be prepared: Tekumel is a very rich milieu and can take a long time to get one's head around. Do some searching on the 'net, and you should find plenty to keep you busy.
This message was last edited by the user at 19:20, Mon 27 Feb 2017.