This is an interesting question, because novels such as this one that are set far into the future automatically are going to seem strange and implausible to us because the level of technology in such a novel is so much more advanced and sophisticated than the levels of technology of our own world. However, we could argue that the author does a good job of projecting what we think we might achieve in a few years time into the future. This novel is set at a time when space travel has become commonplace and colonising the planets around earth is not just a theoretical possibility any more, but something that has already been started. It also depicts a future where contact has already been made with alien lifeforms. None of these are aspects of the future that seem too impossible given where we are now and what could happen in the future.
I think what makes such details more realistic is the way in which the novel focuses on the character psychology of Ender and other key individuals, and describes their human emotions so brilliantly. Even in a world that is so different and so much more advanced than our own, humanity has not changed fundamentally, and the psychological development of Ender as a very tender, sensitive young boy who is trying to work out what is happening to him and why is a particularly convincing portrayal.