I believe that Isuzu did not change the angle of the windshield. Rather, they just shortened the total length of the windshield perhaps to not only lighten up the load pressure on the pillars, but also to minimize the wind drag as well. As you can see, for demonstrative purposes, the following photos showing the windshield remaining the same angle except for it's shortened length on the O2. I know that the angle of the photos of each vehicle slightly differs. But, you get the point.
The idea of using the "B" rear side pillar as a rollbar doesn't seem too far fetched. I can see an integrated welded 3-4" steel tube right underneath that section, which will be concealed by the pillar, that would run from the chassis to and around the roof line and back down to the opposite side. This will leave plenty opportunity for keeping the rear seats in place and redesign the rear covered trunk area with an integrated rear wing similar to the O2. I also can imagine a hard shelled fiberglass removable top for the rear half combined with a T-top with removable panels up front being a viable compromise to achieving the O2 look while still being able to use everyday.
Definitely worth brainstorming about if this topic goes further than discussion.