I prefer the phrase general theory of systems. That is closer to what we intend for what was originally expressed in German by Ludwig von Bertalanffy. But this would transform the very popular abbreviation GST to GTS. Throughout this website and texts on the SPT we insist on using GTS. Part of this is due to our attempt to overcome early and loud criticisms of the GST movement. Some experts argued that there is no such thing as a GENERAL system; that all systems are instantiations. They were correct in a limited way and turned many away from GST attempts. GTS avoids that conundrum. However, if we do find a consensus that agrees on a general theory, then that single theory would be a general system. Ironic.
But that would take the willingness for humans who are so focused on particulars to allow the abstraction across all system instantiations (particulars) to find and recognize and provide evidence for similarities across most systems.