Project management is, for the most part, less of a science and more of art. Therefore, I believe that categorizing or formalizing the practices in project management is extremely difficult and unifying even more. The point of view is that project management is less of a theory and more of a practice, but this practice can involve the use of several systematic tools that have been used and proven to be efficient. Project management can be broken down into knowledge areas such as time management, scope, cost, HR management and etc. These aspects exist in many diverse settings but the knowledge of best practices if applied should lead to an increase in project success. Unifying concepts of project management practices that would guarantee universal success across disciplines sounds very difficult to me. And I think that is why PMI is starting to appreciate agile practices more and more compared to the traditional project management theories.  

I believe a unified theory for PM can only potentially exist in a very general form. For example, the text for the course, the PMBOK Guide, discusses PM techniques in a general form but within any specific company these would have to be adapted based on the needs of the specific industry, such as a PM in a medical device needing to follow the FDA requirements that a PM in a civil engineering company would not. A unified theory would not be suitable for PM across industries. 

In addition, a unified theory would often not be suitable within an industry due to variance in projects. A PM on a class I product development project would not be able to follow the same practices as a PM on a class III product development project due to significant differences in the regulations each must adhere to. 

Overall, due to major differences between industries as well as between projects within the same industry, I do not believe a unified theory for PM would work in anything more than a very general sense. I agree with the researcher mentioned in the initial post that a unified theory would not be successful due to the context-specific nature of projects.