The theory is plausible, although it reflects a rather static conception of the Self (as if changes were only accidental to it).
On the other hand, Mīmāṃsā authors developed a theory of bhāvanā which seems not to differentiate between bodily and mental actions. In this way, they can make sense of Vedic prescriptions as exhortations to action even in case one does not immediately perform the action enjoined. Someśvara (12 c.?) explicitly says that prayatna is a kriyā. On the other hand, Rāmānujācārya lists it together with the guṇas. But, he also says that bhāvanā is prayatna (!). This might mean that a certain point of the history of Mīmāṃsā confusion reigned in this regard, or that Mīmāṃsā authors just repeated the list of guṇas they found in Nyāya texts, without thoroughly reflecting about its implications.