This is a new book by Kate Crosby which addresses Esoteric Theravada. Southern Esoteric Buddhism - Wikipedia
Though, of course, this is not about Early Buddhist Texts, arguably it is relevant to understanding the creation of the modern meditation movements that many of us have learned from and been influenced by.
Esoteric Theravada - The Story of the Forgotten Meditation Tradition of Southeast Asia
By Kate Crosby
Theravada Buddhism, often understood as the school that most carefully preserved the practices taught by the Buddha, has undergone tremendous change over time. Prior to Western colonialism in Asia—which brought Western and modernist intellectual concerns, such as the separation of science and religion, to bear on Buddhism—there existed a tradition of embodied, esoteric, and culturally regional Theravada meditation practices. This once-dominant traditional meditation system, known as borān kammaṭṭhāna, is related to—yet remarkably distinct from—Vipassana and other Buddhist and secular mindfulness practices that would become the hallmark of Theravada Buddhism in the twentieth century. Drawing on a quarter century of research, scholar Kate Crosby offers the first holistic discussion of borān kammaṭṭhāna, illuminating the historical events and cultural processes by which the practice has been marginalized in the modern era.