Don't hold your breath waiting for Maiden to be inducted. I'm almost positive it won't happen. Sabbath was obviously deserving of the honor, based on their widespread influence if nothing else - even metal-haters I know agree with that. Yet the HOF ignored them, while inducting people like Percy Sledge (who's been milking one god-awful song for 40 years, and has done nothing else that's noteworthy).
The HOF inductees are chosen by rock critics - old critics whose "credentials" date back to the 1970s. The type of critics who have never respected metal or progressive rock. (Notice how they haven't inducted Yes, who hold the same status for progressive rock that Sabbath does for metal. Or Rush, who are also deserving of induction.) These type of critics will never give Maiden the respect they deserve.
The only metal band with the slightest hope of induction is Metallica - and that hope only exists because Metallica have gone mainstream in the last 15 years.