Up until now I would have expected them to hold off re-releasing these films as special editions until Mad Max 4 came out, so that they could do a promotional tie-in with the new film. However, Mad Max 4 appears to be dead again according to recent reports... it could be another 3-4 years before it finally comes out, if ever. I hope MGM changes their mind and gives us special editions sometime next year.
Don't believe everything you read in Variety. They created an article about Mad Max: Fury Road being dead from the news that Mel Gibson was now developing a new film titled Under and Alone. What's lovely about the "article" is that it doesn't mention how Fox already announced production was pushed back to 2004 with the initial setback nor did it seem to check sources or gather quotes from Fox (the studio producing it), George Miller or Mel Gibson on the matter.
Some magazine recently interviewed Miller, who mentioned how Fury Road was still in development... sending people who read the Variety article into confusion. If you read it as much as I do, you can see they're not very good at fact checking. They run their own speculation, much like the rest of the Internet, and typically regurgitate press releases without making sure the studio statments are true or make sense (see the announcements involving New Line's Texas Chainsaw remake or Universal's Van Helsing).
Anyway, the problem is that Fox may not have an economically viable shooting location. Africa fell through after the war in Iraq took off and Australia's exchange rate is still a bit steep for their production. If it does happen though, Warner must decide if special editions will sell as unofficial tie-ins to coincide with either the film's release or it's own DVD. That's a lot of if's...