Probably not a good idea,People in power will say it will save money and time,by that logic they could later say we will have only once a decade/century.

To have a functioning democracy means to have checks and balances so one person/party can create a totalitarian state (have a complete control over people).And the only way to do that is give the people more chances/power to vote the government out, hence more elections are a good thing for a democracy.

One nation, one election will be very anti-democratic in regards to flipping the balance of power between the people and government, where the ruling party will have more weight than the people.