And we start hitting the length-creep phase for the... less conventional epilogues.
Epilogue
It isn't so much that Sokka ever became closest to the Mechanist or Wang Shi Ton or anyone else above everyone else, but rather that with their help Sokka became closest to himself.
In so many respects, Sokka was not fit for the world he was born into. A staunch dis-believer of magic in a world of spirits, a devoted advocate of science in a world where scientific principals had barely been breached, and so much remained unknown and unexplainable. But Sokka believed in it, clung to it, even as he would not believe, would not submit, to the ideas of spirits and the unknown. In so many ways, he would have been better born a hundred, two hundred years down the road.
In his mind, the only element he needed to bend was surprise: surprise the crowds with fireworks and flash-bangs from oh-so-conventional oils and chemicals. Surprise his friends with his abilities to forage and hunt food without so much a flicked wrist of any element. Surprise the scams and gamblers with his superior understanding of chance and numbers.
And, of course, surprise his enemies with the oh-so-primitive-yet-dynamic boomerang-from-behind trick. Gets them every time.
But the Mechanist, and Wang Shi Ton, and his travels, opened his eyes to how much more could be done. He felt guilt, deservedly so, for being so instrumental in developing the war balloons that the fire nation later used to advance their conquests. He knew his weapons, his tools, his knowledge, could be used to cause great misery.
But that was always the people behind the machines, not the machines itself. Machines were like knowledge, themselves inherently neutral. It was the person behind the usage that mattered, and the machines could do so much good that it hurt to see that no one would consider them.
Like the lunar calendar in the library: just imagine the scientific applications! Or the fire nation's metal ships: the poles were filled with coal waiting to be mined, and metal ships could carry in so much more food for the villages. Even Omashu, Ba Sing Se, or even the Fire Nation's navy proved that bending could be incorporated with machines and machine principals to do so much more than either alone! His invasion force, as bloody necessity as it had been, had been a beautiful fusion of science and spiritual progress!
Oh, the Fire Nation. To think he once hated them so blindly: they might have been a bunch of racist egotistical jerk-faces, but they hadn't been wrong when they thought their machines were the promise of the future.
His friends were great, and he loved them all very much, but he had this idea for a new carriage that could drive itself, and he was sure that he could work out the kinks if no one would bother him for just a few more days…
After the war, Sokka failed to settle anywhere for long, and found himself traveling to various parts of the world, studying various technologies and ancient devices, and endlessly trying to improve upon them, his efforts gradually gathering to him a small but committed band of disciples. When he wasn't dragged out of his lab by his friends to help save the (or just see the light of) day, or being reminded by his assistants to eat his food and put on all his clothes before trying out a new idea, Sokka gained a reputation as an eccentric genius who's benign inventions ultimately brought great progress and and benefit to the world, lionized and romanticized by history as the archetypal genius of many fields, from war to art to flight and other advanced technologies. Much of his work was funded by King Bumi of Omashu, recognition of value from one mad genius to another.