From the Truth About Cars (and not a lot of actual details, obviously):

“We will have to dig more in the U.S.,” he told Automotive News. “But when you talk about purchasing, engineering, platforms, engines, plug-in hybrids — it’s massive.”
[...]

“The day we announce the deal, we’re going to tell you exactly what we’re going to do together. And it’s massive. It’s massive between Mitsubishi and Nissan,” he said.
What is it? It's MASSIVE! MASSIVE, I TELL YOU!

Source: Ghosn: ‘Massive’ Plans for Mitsubishi-Nissan Alliance in US

See Thread: Nissan to take control of Mitsubishi following fuel economy scandal