Hi rooster - basically what Don said.
The place is fairly fast moving and typically you will get responses in minutes to most questions. Your exact same suggestion has come up at least one other time by somebody else.... and it died pretty quickly. That's not a criticism and it's not a bad suggestion; just that POTN's don't seem to function that way for the most part.
I do see a major disadvantage though. "Chat" tends to be ephemeral. Actual threads and topics can be easily searched, noted, and references. I don't believe you'd be able to handle chat well in that fashion. A lot of really good stuff gets discussed here, and checking topic headers is a nice way to find things.