It all depends on your stove.
I've used my 8 gallon 14" wide pot for "full" 6 gallon extract boils on a "Kenmore" and could keep a rolling boil when bridged over the 2 largest elements, but had to keep the lid half-on most of the time. No DMS problems.
On my new Samsung with a triple 11" element I can keep a full 7 gallon all-grain rolling boil, also with the lid on half way but now part-time. For a 5 gallon volume I can keep the lid off.
I've bubble-wrapped (Reflectix) the kettle and get a bit more heat efficiency. It really helps against heat loss. Just make sure not to burn the plastic to your stove or SWMBO will be very unhappy.
The problem is the elements have their own temp sensors and shut off before they max out their capacity. I guess that prevents problems later on.
Make sure there is no grit, sand or other material between the stove top and your pot bottom, or you may crack the glass. It needs to be really smooth and clean. A perfectly flat, triple layer bottom is best for conduction and prevents scorching.
You would need a 240V, 3500W "induction plate" to boil a kettle of that volume. The 120V, 1800W versions are not sufficient. It maybe a better and cheaper solution to mount a heating element in your pot. Lots of threads about that here on HBT.