There is no scientific basis for warp drive, replicators, levitating cities, or aliens whose only distinguishing trait from humans is a forehead wrinkle, but all those things can be found in the science-fiction genre, hence the word "fiction."
Well, except for the forehead thing...I'm forced to disagree...In D&D they have pointy ears.
Replicators rearrange energy and matter into desired patterns- which is what happens in biological, chemical and nuclear reactions. Its not a question of could this be done, but HOW it could be done in a controlled fashion. According to the big brains out there, energy and matter are interchangeable-its a question of changing states.
Warp drive/hyperspace etc., in some form of another has been theorized not only by sci-fi guys, but also by serious theoriticians. Usually theories about warp drive (and its close buddies teleportation and time travel) involve hypermassive bodies like black holes or neutron stars...but others have described it as a possibility with string theory.
Reality? No...at least
not yet. But
possible according to some serious thinkers.
Compare that to terrestrial giant fire breathing reptillians: Never have existed- never will. And while there are some truly exotic animals out there, we have never found anything out there as exotic as the majority of the inhabitants of the MM's, Fiend Folio, etc.
That "not yet" as compared to "never have never will" is crucial. Its not a bright line test- after all much of the tech we use today would be considered impossible to someone 200 years ago- but it still points at a qualitative difference.
On the other hand, as Arthur C. Clark said: "Any significantly advanced technology is indistinguishable from magic." Many authors like Larry Niven, Heinlen, Moorcock etc. have played with that perception.
Add to that the recent move by WoTC to make Illithids into invaders from the future....
With that in mind, I really can't rule out psionics/psychic abilities as somehow "inappropriate" to a fantasy setting.