Definately cool, but didn't Mazda prove pretty well that breakthrough technology doesn't really do much unless you have pretty much universal acceptance.
If you're referring to the Wankel, the only reason Mazda's kept that around for so long is because the president of Mazda was good friends with Wankel. Wankels have some nice performance aspects to them, but they're overshadowed by the problems with the engines. They don't burn nearly as clean as your basic internal combustion engine, and don't handle wear and tear quite as well. They have their uses, but Wankels never had a shot at replacing your standard internal combustion engine once emissions laws came into play, which is why GM abandoned them.
They also get pretty bad mileage. Fuel costs in the 80's forced mazda to switch back to reciprocating engines in all but the rx7.
The problem with engines like this, and there's more than a few of em out there, is that they trade reliability and "robustness" for efficiency. By the time they reengineer the thing so that it lasts more than 20,000 miles in the car, you lose all the benefits it had.
