I’m with Sean on this one. Getting the heat transferred into and out of the metal is more critical for fast heating.
An interesting idea would be the adoption of the JetBoil design for a brew kettle: http://www.jetboil.com/products/technology
where a series of meal fins provide a larger surface for the fire to metal heat exchange. This makes for more efficient use of the heat from the burning gas.
Another aspect of fast heating is even convection in the kettle. This is not necessarily given when we bring wort to a boil. Because all bottom of the kettle is heated evenly the hot wort wants to rise upwards from all these places. Unfortunately the cold wort that is falling down from the top gets in the way and there are many turbulences and the all so familiar sudden rise of large bubbles.
An improved kettle design would heat the kettle only in the middle or offset to one side. By doing so you promote a more even convection of the wort and better heat transfer between kettle wall and wort. But the more you move the burner off-center, the less heated bottom area you are providing.
Yet another thing that gets in the way of good kettle wall to wort heat transfer is the formation of steam pockets/bubbles on the kettle wall. Those end up creating small spots of insulation between the wort and the kettle wall. That’s what you hear crackling when you are heating the wort. As soon as you stir the wort this crackling goes away since the hot wort close to the heated metal is replaced with colder wort. This is yet another reason why good convection helps with heating wort faster.
All this being said, I brew with a 5 gal SS pot that has none of the enhancements I talked about. Maybe someday when I have a new burner stand I can try off-center heating to see if it improves convection.
Stirring the wort while heating is an elegant option as well. Especially you have a motorized stirrer which you could also use during the chilling process with an immersion chiller. Or you may want to keep the pump running while you are heating the wort. But make sure that the heat loss in the hoses is less than the gain you should be getting from better circulation in the kettle.