loved my 6mps, but they're now getting long in the tooth and some older mps engines seem to gone pop with stretching timing chains in the last few years. I spent ages trying to find as pristine example as I could, but it still cost a bomb with upkeep, even simple jobs became problematic as all the rear drivetrain parts were so rare/unique and a lot of Mazda's documentation still called up the std 6 components despite the awd system on the mps. e.g. an abs sensor went flaky, so asked Mazda parts for one, but didn't fit (as it was the 1 for the non mps). tried another, nope. mazda were insisting they had provided the right part, and would only fit themselves with a diagnostic - turning it into a £250 job...
With new rear diff mounts, TIP and intake, Cobb (and tune from the infamous "Justin" in the mps scene) it's a beast of a sleeper...
I thought the proposed new 3mps was awd, so being almost a cross between the existing 3 and 6 mps. There seem to be fewer and fewer "hot" saloons, so I can't imagine them risking another 6 mps as a saloon - but you could imagine a coupe version?
There's a massive market for these cars, especially in the States as I believe the Mazdaspeed (mps) are v popular there, but that doesn't mean they can justify designing a new car. Look at the rotary cars - RX7 and RX8 popular but afaik they've said they're not developing the good old Wankel any more.