I believe they are cast steel so you should be able to weld a gusset. I've thought of that, but have never gotten around to checking clearances and what would be able to fit. I know Toyota guys have to do it since their spindles are even thinner.
Haven't had to bring the truck in for warranty since I've had parts installed. I'm sure anything transmission or anything after transmission on the drivetrain, they'd really kick up a fuss about. Truck is already at 36k miles so I only have powertrain warranty remaining on the truck now.
I'm curious if the ZR2 front diff will be an easy swap to non-ZR2 trucks. I'm hoping it means that companies will start making gears for the current generation front differentials though. I'd really like to swap to 4.10 gears, but there still is nothing available for the front differential. I don't personally know anyone that has bought a ZR2 or AT4x though.