I had to chuckle when I read this part... In the LR3 world, everyone is adamant you NEED E-rated tires! E-rated tires are rated for over double the GVWR of the the 3. I have had one person in 4 years agree that E is overkill. Plus few seem to grasp that an E rating does not guarantee a truly tougher sidewall.-Most of the 35" off road tires I like are only available in E-Load Range; so airing-down is almost ineffective as the 10-ply sidewall barely deforms as the pressure drops. Even the D-range tires available are heavy as hell. Have not been able to find any 35" XL range off road tires.
I believe I heard on the Overland Journal podcast that the designers had 35's in mind when designing the new Defender. If I'm correct in my recollection, they're a source I trust and the running gear should handle it fine.
That being said, my opinion is 35's would be overkill for what I personally would use the vehicle for. I don't view really any Land Rover as a true rock crawler, but definitely one that can handle it occasionally. With the independent suspension and 33's you will crush the ground clearance of pretty much anything else on 35's without a lot of the headaches. Put on some sliders to protect the rockers and let the control arms get their battle scars!