It’s not a good idea.
The KDSS anti-sway bars, both front and rear, are much, much thicker than really anything else out there. Stock or aftermarket. They can be like that because of what KDSS is, an automatic inertia driven hydraulic system that can release when needed. As such, the KDSS anti-sway bars barely twist under load. Any real twist of axle articulation comes from the hydraulic cylinders releasing instead of the bar itself twisting. Like on every other anti sway bar design.
KDSS is quite phenomenal, it has zero inputs from anything. Nothing tells it you’re off road, on road, in low range, going 100mph. It’s a purely separate system of the entire 200 and how it knows when to lock and when to unlock, without even knowing vehicle speed is just astonishing.
The body roll you are feeling is the engineering limits of a modern body on frame 6,000 lbs + SUV with a live rear axle.
This is why the Sequoia is a little nicer of a highway riding SUV. It has an independent rear end, which yields much less body roll. Flip side, independent rear suspensions suck off road, with the exception of an H1.
I’m sure the upcoming 300 series will be even better on road while somehow getting better off road, just as every land cruiser has been.
Yet for trying to “upgrade” a KDSS bar, not going to happen. No one makes one, and how much thicker can it go? 50mm? I mean, I consider myself the nay-slayer, and try almost anything, but sometimes physics and the cost-benefit ratio of modifications are not in our favor.
I’m not one for increasing spring rate, just for cornering ability unless it’s a track car. That said, that’s the only option out there. Get rid of the soft factory springs and stiffen up the suspension, while also forced to lift the truck. Which will in turn, make body roll more significant.
I’m not saying you can’t put thicker bars in a KDSS truck. But you’ll need to find someone who can make them, and have a good amount of money.