A common definition of the introversion/extroversion axis is whether an individual is prone to over- or understimulation, leading them to seek out conditions that help them modulate sensory input to desired levels.
Rarely, at least in these words, do I hear about introversion/extroversion in the context of output. It seems fairly obvious to me that individuals vary in terms of how much interaction they require from their environment to remain engaged and not put off, and this expresses itself in people’s differing tendencies to write versus read, play games versus watch television, and talk versus listen. In many ways this axis seems much more interesting and consequential than what we currently measure as I/E, considering the implications for job suitability.
A possible objection to this addition to the introversion/extroversion family is that I/E tends to be relatively stable over the life course, while at least anecdotally mental activity levels can vary widely by circumstance. I’ve found that hypomania pushes my talkativeness and written output up, while obviously depression dampens them, but these states can also easily affect more “established” personality facets, and I’m unsure of the degree of variability non-bipolar people exhibit normally.
I also have a sense that at least a non-trivial fraction of people experience the tendencies to produce and consume as strong opposing forces, such that a person who had a very easy time of thought generation might find it difficult to read, and a less mentally active person, when faced with a blank page, might resort to reading condiment labels rather than try and dredge up thoughts of their own. I would also guess, partly from my own experience with expressiveness as characteristic of hypomania, that people higher on the production end would show a stronger tendency toward anxiety than depression overall, possibly reflecting a difference in something like endogenous energy levels.