[@CollectorOfMyst] Hardly. Republic City had an electrical power plant (supplemented by lightning benders), and there were internal combustion engines powering cars, trains and motorbikes. The early mecha suits and planes were also internal combustion engines, though I couldn't tell you what the later Earth Empire ones were powered by. If it's any -punk, it's [i][url=http://tvtropes.org/pmwiki/pmwiki.php/Main/DieselPunk]dieselpunk[/url][/i], which is 1920s-1950s.

Given that Avatar Aang lived for just about 66 years, and that was young, we can safely say Korra's lifespan would be somewhere around 90-100 at most. Taking the earliest date (1920) and the youngest possible "old age" death for Korra, we're looking at roughly 2000-2010. If the Avatar world follows a similar technical path to our own, they have modern or better technology. If there isn't a major technological boost, like WW2, we're looking at 1980's level technology in Republic City, with other cities close to or equal that.

Avatar "Rosai", the earthbender after Korra, would live in a world not unfamiliar to people in their 20s or 30s grew up in. We'd have an Earth Federation (United States of Earth?), two independent water tribes, an Air Nomad society with nonbenders (classism?), a (partly speculation) Fire Nation grappling with constitutional monarchy, and a democratic United Republic. On top of that, you'd likely see an almost complete homogenization of bending, with your place of birth being almost entirely unrelated to the bending skill you possess. A firebender born at the South Pole, for example.

So if we go into the "next Avatar", we have to do our own worldbuilding. A unified idea of the world would help with that.