In terms of what I mean by 'ego' is the rational (formop) ego. Cook-Greuter lists various stages of 'ego' development in the usual broad range. Or what Damasio might call the narrative self in distinction from the proto self or the core self. Thompson also explores Damasio's ideas through what he calls ipseity. And I'm taking my cue on how the rational ego looks back to go forward from Washburn, Goddard and Levin, cited earlier in this thread with links. This egoic process (it is not a static entity) is precisely what you describe as "advanced forward brain systems" capable of neuroplasticity, which indeed "exceeds what most people would accept as the definition of ego." I'm not using "most people's" descriptions here but the more precise definitions of my neuroscientific, and meditative in the case of Thompson, brethren.
Recall Levin from this post:
Body Levels: 1 - primordial; 2 - pre-personal; 3 - ego-logical; 4 - transpersonal; 5 - ontological.
"Development from stage 1 to 3 is normal and typically completed when the child becomes an adult. Stages 4 and 5, however, represent stages of individual development that require special effort, commitment, and maturity. Stages 1 and 2 are basically biological. Stage 3 is distinctively cultural.... The ego-logical body is the body shaped according to the ego's image of itself. But stages 4 and 5 go beyond what society requires. We might call them 'spiritual' stages.
"Normal development (stages 1-3) is always, more or less, a linear progression, but the progression beyond 3 is not; it is essentially hermeneutical, involving a return, a turning into the body of experience, to retrieve a present sense of the earlier stages. Beyond 3 it is necessary to go 'backwards' in order to go 'forwards.' Stage 3 is the moment when, for the first time, this return and retrieval is possible."