Probably ought to remove the glass roof first...
We should dig up roll over crash photos. I've seen many of Discovery 2 that weren't so nice but also pretty messed up recent modern G wagonsfr high speed shenanigans. I do wonder how the unibody would fare minus all the glass it would release. Those big 3rd row windows too, wow what a mess it would be.
I've seen an LR4 on its lid here in Hawaii and it was not a pretty sight. I also do not think it was high speed and not sure exo-cage would have helped; all windows on that side and hatch busted.
Believe it or not, on a unibody, the body skin adds quite a bit of structure to the rigidity of the chassis. Cutting into for the exo-cage mounts might actually weaken it in those areas.
Although, I would think a good bumper, sliders, and rear bumper with the side slides might limit some damage if it didn't go all the way over.