We still have quite a bit to learn from the German Idealists about systems, and system-building, about the nature and limits of systemic thought. Perhaps the greatest lesson of the German Idealists is that 'system philosophy,' also commonly referred to as 'systems thinking,' systemics, or 'systems theory' (to be distinguished from the sociological systems theory of thinkers such as Niklas Luhmann), etc., encourages both good scepticism toward already-received knowledge, challenging thought's tendency to get locked up in intractable aporias or the doxa of everyday opinion and offers the type of synthesis of the special disciplines that unites our knowledge so that it might be coordinated and applied for a diversity of practical purposes. System philosophy ought to be distinguished from the system sciences, however, because system philosophy maintains a critical stance toward the results of scientific research. Where system sciences collect knowledge, system philosophy asks about the _significance_ of this knowledge.
Systems philosophy in the 20th and 21st centuries has been partially obscured by the dominance of systems sciences and their 'theoretical' practices. Klir (1965):

The concept of system is one of the most widely used concepts in science, particularly in recent times. It is encountered in nearly all the fundamental fields of science, e.g., in physics, chemistry, mathematics, logic, cybernetics, economy, linguistics, biology, psychology and also in the majority of engineering branches. We are concerned with a very general concept.

System sciences grew out of a larger ‘unity of science movement of 1920s-40s.’ Systems philosophy in the 20th century was able to benefit from this movement, rejuvenating itself by consulting the theoretical efforts of the so-called ‘General Systems Theory' (Bertalanffy, Laszlo), and the researches of the cybernetics and information theory movements. General Systems Theory (GTS) called traditional scientific concepts of linear causality, determinism, and reductionism into question and replaced or supplemented them with notions of circular causality, self-organization, indeterminacy, and the unpredictable emergence of order from disorder. GST worked toward developing a unified theory and methodological approach to investigate not just the classical simplicities of the mechanistically structured material world, but also the complexities of biological, cognitive, and even social systems. Systems philosophy at the current juncture is informed both by the past (the insights of German Idealists, etc.) as well as by continued research in the sciences (and of course the 'system sciences' whose research is specifically guided by the concept of system).