The warp drive article depends on 'exotic material'. Therefore I could sketch out the most Amazing Fantastic Engines and provided exotic material was the essential component they would be plausible.
Exotic material which is quantifiable, measurable, and describable in purely scientific terms.
Was "enriched" uranium "fantasy" before we had the tech to make it? Was steel "fantasy" when all we had the tech to make was iron? Obviously not. There was nothing scientifically implausible about either...we just lacked the means to implement it.
Same with "exotic matter". We may not be able to make it (yet), but we know what it must look like and what properties it must hold to be suitable for our purpose.