Freeciv

Though, if easy, it would be even better to have more generic "MinStoredOutput" and then use "OutputType" "Local" requirements

Likely, not easy, that requirement vector should be recalculated with different output types in context to fire, where do we have it? If some actions or effects has a requirement for accumulated gold/shields/luxury, we most probably are interested in its value relative to something (cost of production or advance, another player's wealth, city population...)