You don’t need to know each individual’s preferences/productivity, you just need a good guess of the aggregate across the population. The numbers don’t change much month-to-month, and in any case there are pretty good forecasting tools. Same with productivity — in aggregate everyone will be about as productive as they were last month (seasonally adjusted).
When you get demand wrong, you’d just deal with the short-term imbalance by varying prices. There’s no reason why a communist economy can’t vary prices — state-owned airlines do it all the time.