The role hasn't been specified yet, and it isn't known if he will play a villain. But It will be a "lead role" in this upcoming sequel. Deadline New York did speculate that it would be a "reasonable assumption" that Tom Hardy is gearing up to play one of DC Comics iconic villains.
Tom Hardy is still attached to star in Mad Max: Fury Road, although we reported just last week that production has been delayed on this particular reboot until 2012. The actor remains attached to the project and will definitely star when the production is ready to go before cameras.