It's unsure if it will replace the K10D entirely or if it will be a level above in the product line. Some are saying that K10D production has ceased but I've not heard anything official. Also the current K10D price fits nicely between the new K200D and the speculated street price of $1,200-$1,400 of the K20D.
And to address abstract's post, nothing is for certain yet but high ISO performance is one of the things that those in the know about this camera are touting right now. Maybe not D300 like performance, but not far off supposedly, and from a 14 mega pixel sensor!
SLC