Bark's Bites: The FiST Is a Rollover Risk, and Some People Don't Want You to Know | The Truth About Cars
I thought this was a pretty good article describing what to be concerned with
"The problem seems to begin when you start messing with things that affect the grip level of the ST. In Simmons’ case, he only changed two things about the car, but they were significant: a stickier tire and a smaller wheel diameter, both of which change the behavior of the car in ways that can’t be perfectly replicated at Dearborn’s testing grounds. There’s talk that the smaller diameter of the FiST’s front sway bar (it’s actually smaller than the regular Fiesta’s) might be the culprit – any serious national-level autocrosser will replace it nearly immediately."
edit: just so I don't get flamed, this is an incomplete analysis. there's a thread here you can read but if it's the same incident, the driver's tires also had a very soft sidewall AND the springs he paired with it were a HUGE no-no. He basically created a suspension that would catapult the car under load followed by sudden unload.
I don't think Forum users here "like to gloss over it" as one of the super users has his profile picture of his car WAY up on two wheels through a chicane. Getting up on two wheels is a definite possiblity and has been documented everywhere (go look up Top Gear's initial review of the FiST to see Clarkson lift a tire through their road course). Rollover is a concern for sure but no more so then it is for a Mini (like what happens in the article).