A TV special promoting the release of Part II (seen above and, yes, hosted by Leslie Nielsen of Naked Gun fame) featured a part (about 25 minutes in) where Zemeckis talks about the hoverboard technology and says, "They’ve been around for years. It’s just that parents' groups have not let toy manufacturers make them, but we got our hands on some and we put them in the movie.”
Zemeckis delivered the line with a sly smile that indicated he was kidding, but most kids wouldn't pick up on that subtlety...and didn't.