If we can do this eventually, then perhaps we can make our way to models that capture a larger fraction of the truth and can be tested against reality.
Nonetheless, many of these models are still falsifiable. For example, the textbook model of the benefits of trade due to comparative advantage only contains two countries and two goods. Although extremely simplistic, the theory does have falsifiable predictions and there is good empirical evidence supporting the broad theory. But this simple model will not be able to accurately predict how much a particular country will benefit from free trade.
Even if you did have all of that data, you would still be missing a lot of data. For example, an important factor in economics is asymmetric information. An actor's decision may be optimal given the information available to them at the time even if the decision is suboptimal given perfect information. So for an even more accurate model, you would also need to have data on what each actor knows at any given point in time.
Furthermore, an actor probably does not have the ability to calculate the optimal outcome given the information available and there are innumerable subjective factors in economic decision making.
Big data will help you find some kind estimate, but it will not suddenly make economic modelling simple.