I'm considering writing a fantasy novel. While I'm striving to make the world as original as I can, and not rely on many of the popular fantasy tropes, for the purposes of this question you can assume the world is your traditional fantasy setup: elves, dwarves, dragons, magic, wizards, quests, all that.
Because I cannot for the life of me stop worldbuilding, my insatiable need to design has expanded beyond the confines of my fantasy world. There are other alien species. Advanced technology. Spaceships. Defensive shields. The whole nine yards.
I would like to incorporate some of these ideas into my fantasy novel. I think, if the novel is successful and popular and the publisher agrees to a series proposal, the little hints that there is more beyond the fantasy world could tantalize readers into speculation about exactly what's out there, and the true nature of things. That speculation could in turn boost sales and popularity, which the publisher would love, thus creating the need for more novels. Hence my plan.
Don't worry, I'm not assuming this will happen. I know this is all speculation.
Now, I know not to sell something as fantasy and give my readers sci-fi. At no point in the novel(s) would I explicitly say something is high tech, or of alien origin, or that the star people see moving oddly is in fact an orbiting space ship. It would be on a level the inhabitants of my fantasy world could understand. Strangely moving 'stars', a 'rock' or 'metal' they've never seen before, or even a mysterious new creature which fell from the heavens in a fire ball and died shortly after. That type of thing.
Now to the reader, it's obvious that these things are not of fantasy origin. They can easily put two and two together and realize that there are orbiting spaceships, alien species, and perhaps even a whole galaxy full of life going on outside the little fantasy world. Would this be a problem?
Would my fantasy readers be displeased at being drawn into sci-fi, even though it is never really defined as that? Or would such hints at sci-fi only encourage curiosity about what's really going on outside the world? I realize readers will go both ways, but I'm looking for what the majority would think.
I realize this is very open to speculation, so if you have any sources, please cite them.
EDIT: The answer provided by Phillip, while not a true answer, does provide some excellent advice for anyone else with a similar problem.