Replying to a tweet by a curious gamer, Avalanche Studios' Christofer Sundberg revealed that Rage 2 is developed on the company's proprietary Apex engine, so it's fair to assume we'll see an open world carnage in the ilk of Just Cause 3.
Sundberg's full reply was "Avalanche Open-World Engine", which would be in line with the developer's earlier work. You may recall most of their games built on what they call Avalanche engines, so we guess it's more of the same with Rage 2.
Unfortunately, Sundberg refused to divulge more, most notably when asked whether Rage 2's Apex features id Tech 6 or if it's entirely an in-house design. It's not hard to see where he got the idea - id Software literally begs that question.
ZeniMax's ownership of id Software and their insistence on making id Tech 6 available only to the companies they own, which includes Bethesda, would further suggest the link but it appears it is not the case. After all, John Carmack's departure did somewhat degrade id Software from doing groundbreaking work on a regular basis to merely a company doing work.
So, it's pretty much certain that Rage 2 will follow the original's recipe, only this time at an even grander scale. Having said that, the recipe better be improved upon on the qualitative side of things too, because Rage simply lacked connective tissue.
It is said that Rage 2 has already got quite a few car gameplay experts working on the vehicle side of things, even though Mad Max, Avalanche's earlier game, seemed to have nailed that down pretty well. Either way, we should know more when Bethesda, Avalanche and id Software's Rage 2 debuts on this year's E3, when we should get a proper taste of the sequel's gameplay.
Rage 2 initially leaked via Canadian branch of Walmart, who apparently didn't really make a mistake, more like jumped the gun. Bethesda had a hilarious response as well, giving Walmart some tips on how to accurately mimic Rage's style. Well, we guess it may come in handy when Rage 3 rolls around.