I agree with what you say about rotating inertia but just the sheer added weight is a huge deal. I work with a bunch of guys that go muddin and they have large tires too (though in a different fashion) their tires can weigh up to 200# each. this can add 800# to the car. that within itself would need a brake upgrade I would think.
not sure about mass. but in VA the factor is the height of the bumper and many get away with it by either adding a second bumper that is low enough or just relocating their bumper to the legal height.
Be the change you wish to see in the world
Boggers that weigh 200 pounds each replace OEM tires that weigh 40 pounds...your math is a little off, that would add 640 pounds. Anyway, donks get tiny tires on those huge rims. I'd be more worried about the leverage of the extra diameter with 26 to 30 inch wheels, totaling 28 to 34 inches vs. the 26 inch tires that might have originally been on the car.
I don't know enough detail about MA's law, but in RI a drop bumper won't help. From the RI motor vehicle inspection manual:
Vehicles that appear to be altered by elevating or lowering the chassis or body height by more than (4) inches from the original manufacturers specified height by use of lift kits, shackle lift kits, tires, spacers, blocks, tubes or any other means or device shall be rejected unless the owner of the vehicle shows written evidence as to the original height of the vehicle when equipped with the equipment customarily installed by the manufacturer.
I agree with what you say about rotating inertia but just the sheer added weight is a huge deal.
Actually I didn't mention rotating inertia, on purpose. I only mentioned brake force.
You are correct that rotating inertia is a "double-dipper" in the momentum category. Not only do you have to slow forward momentum, but you also have to slow the wheel RPMs (I^4th and all that). That's why racecars will try hard for lightweight rotating components throughout. But when you consider the overall mass of the car, I don't think that the weight/diameter of those wheels will affect things more than a percentage point or two, especially when you remember that at a given MPH a larger-diameter wheel will have lower RPMs.