I can't find an exact answer since all I have found are people presuming what it could be. Has Masashi-sensei ever said what government is set up or has at least given us a hint?
Since you asked for the author's comments on the government, I'll share what an interview with Masashi Kishimoto where this is brought up. It comes from the May and June 2006 issues of Shonen Jump (the monthly version published in America). Unfortunately, I didn't have those particular issues, so I couldn't confirm the interview's credibility myself, but I did find it in several places on the internet. Here is the relevant excerpt:
Shonen Jump: We want to know more about the rest of the Naruto world---what are the normal people like, what are the governments like, is this the whole world?
Masashi Kishimoto: The world outside of the ninja is pretty normal. People make their living by running businesses, et cetera. Konohagakure, the Village Hidden in the Leaves, is the military part of the country. Hinokuni, or the Land of the Fire, provides Konohagakure a place to live, and in return, the resident ninja protect the country as a whole, similar to a military force.
As for the government, the daimyo, or warlords, govern the lands and run the political system and the bureaucracy.
Each country has warlords at the top, and its military has its own leaders. In America, you have a president at the top, but you also have the military general at the top of the military. The states have more power than the ninja, but since the daimyo don't cooperate with each other, I guess coup d'etats happen rather frequently. The world is not yet solid [laughs], but what you see in the story is not everything in the world of Naruto.
Link to full interview: http://narutohq.com/masashi-kishimoto-interview.php
So, what do we know about the governments in the ninja world?
Government in the Land of Fire
The Land of Fire has the Fire Daimyo as its ruler. We see him along with the other great land's daimyo during the Fourth Great Ninja War. There are other lords besides the Daimyo, but I don't believe it is clear how power is distributed among them. The Daimyo could hold most of the power or he could be a figurehead. I expect one of these classifications of government may be appropriate: aristocracy, monarchy, or oligarchy.
Government in the Hidden Leaf Village
The government of the Hidden Leaf Village is made up of the Hokage, the village elders, an advisor, and the Jonin Council. The Jonin Council, elders, and Daimyo all have a part in choosing the Hokage. The Hokage holds most of the decision making power, but his/her advisors and the elders will give counsel. I would classify the Hidden Leaf Village's government as an oligarchy.
Government in the Hidden Rain Village
The Hidden Rain Village's government (under Pain's rule) is a more interesting example. Pain is the sole ruler of this village and he is revered as a deity. He's never seen by the people of the village, and Konan is the one who gives messages. Konan is also revered and is called an angel. This government is a mix of theocracy and autocracy.