WordNet (r) 3.0 (2006):

impracticality
    n 1: concerned with theoretical possibilities rather than actual
         use [ant: practicality]

Moby Thesaurus II by Grady Ward, 1.0:

41 Moby Thesaurus words for "impracticality":
   autism, autistic thinking, awkwardness, bulkiness, clumsiness,
   cumbersomeness, dereism, dereistic thinking, dreamery,
   flight of fancy, hulkiness, ideal, idealism, ideality,
   idealization, imaginative exercise, impracticability,
   inconvenience, inoperability, insuperability, play of fancy,
   ponderousness, quixotism, quixotry, romance, romanticism,
   uncompassability, unhandiness, unmanageability, unpracticability,
   unpracticalness, unrealism, unreality, unrealizability,
   unwieldiness, unworkability, utopianism, visionariness,
   wish fulfillment, wish-fulfillment fantasy, wishful thinking