it is impossible to come up with a model that isn't arbitrary at some step. the lower middle class of today literally live like kings compared to a few hundred years ago, and in a another hundred years the "lower middle class" might very well live like multi-millionaires today.
central planners can not be objective under any circumstances unless it is literally a god AI with perfect knowledge of determinism.
Assuming you mean in the USA, we don't have a democracy it's a republic, which means we definitely do have central planning committees, but they are appointed by politicians who are voted into office by the people. It's not quite "Soviet totalitarianism", but it's several steps removed from voters.
democracy is schizophrenic. if you're saying that voting reflects the preferences of the people we already have a system for that, it's called the market. so under democratic central planning you have people signaling one preference with their dollars and a different preference with their vote. except the majority of people aren't deciding what to do with their own money when they vote, they're deciding what to do with other people's money. producers are a minority.