It is most certainly doable. The question is: is it worth it from a actual cost incurred AND from a fallout effect perspective?

If all of a sudden, one could simply "buy" another account and this was something easy to do, would the player who did not be at such a disadvantage as to decide not to play?

In WoW - probably not.... but most people (99%+) single box as is and I suspect that the vast majority have no interest in doing so. The ones who do (like myself) are willing to accept failures and challenges and come up with unique solutions to problem that are encountered multiboxing. Hopefully, with my guide, people will find it easier to get started 5 boxing - but the considerable cost and complexity will still turn almost everybody away.

Plus, $75+ a month is still, for many people, a nice chunk of change.

So even if you COULD do away with the 2nd or 5th computer requirement (possible with dual+ cores these days) and figure out/provide a robust autohotkey like program to send data to all of the "clients" - would it pay off from a cost to implement AND make sense in that it would retain "balanced" game play?

I can't speak to the first (although I would imagine that it would pay off). The second is trickier. Yes, I "unbalance" gameplay when I 5 box. But, I take up 5 character slots. I spend 5x as much gold. I need to equip 5 characters. Since much of what I do is instance based, I leave most players alone until I start PvPing - which is not what every 2+ boxer wants to do (PvP is HARD to 2 box).

So, perhaps Bliz or another game will officially support multiboxing someday. I fully expect games to eventually embrace gold selling, account transfers, multiple monitor support (hello to you SupCom) and other creative uses of the rapidly increasing and lower cost computer power. I just don't expect it to happen anytime soon.