Hes far left of any current Democrat. I think the powers that be would likely urge him not to run, or at least, not to run seriously. They will probably be putting their weight behind a second Obama term, rather than a new (and far more liberal) voice.
A Kucinich presidency would take us a few more steps towards left-leaning, yet pluralistic governance. It would appease libertarians in some regards, anger them in some. It would anger traditional republicans on almost all regards; and social democrats would likely be opposed (simply because they see it would divide their base).
The center-left democrats would likely not support him, in favor of supporting Obama II.