It usually results in paper or video prototypes, or (more likely nowadays) computer simulations that are as convincing as possible to those that know the relevant science, given the lack of experimental confirmation.
Unlike the scientific method which relies on peer reviewed experiments which attempt to prove or disprove a falsifiable hypothesis, exploratory engineering relies on peer review, simulation and other methods employed by scientists, but applies them to some hypothetical artifact, a specific and detailed hypothesized design or process, rather than to an abstract model or theory.
While both critics and proponents often agree that much of the highly detailed simulation effort in the field may never result in a physical device, the dichotomy between the two groups is exemplified by the situation in which proponents of molecular nanotechnology contend that many complicated molecular machinery designs will be realizable after an unspecified "assembler breakthrough" envisioned by K. Eric Drexler, while critics contend that this attitude embodies wishful thinking equivalent to that in the famous Sidney Harris cartoon (ISBN 0-913232-39-4) "And then a miracle occurs" published in the American Scientist magazine.
On the positive side of the science fiction ledger, the ocean-going submarine, the telecommunications satellite, and other inventions were anticipated in such stories before they could be built.
[1] On the negative side of the same ledger, other science fiction devices such as the space elevator may be forever impossible because of basic strength of materials issues or due to other difficulties, either anticipated or unanticipated.