At risk of sounding like an arrogant academic :) ;Jung DID "coin" the term persona, from the greek (latin?) "per" and "sona" or through sound. The persona, as I understand it, was a large mask with a funnel like device for amplyfying the voice, which Greek actors wore as part of the chorus on-stage. (Jungians are into arcane details - the more arcane, the better :) So, our persona is that mask that we present to the world. So, while your comments about polarities are in essence correct, we really cannot consciously "play out" our shadow on-line, because the shadow is, by definition, unconscious. We can, as we do in "real" life, play with being more introverted or more extroverted, as our ego allows, but we really can't, I believe, constellate our unconscious polarites on the internet.
Just my opinion.