Google is buying up knowledge all the time (eg Frommers). "Knowledge" sites are cheap for Google. Won't be long before they have "knowledge" in every niche. Add that to the open source stuff and yeah Google becoming a knowledge engine is closer than we think.
A good example of this is one "knowledge" area they have dominated for a long time and this is maps. Before Google maps there were lots of sites doing quite well providing maps and mapping information. Google came along and did it better and now dominate.
They can do this in every niche if they want. Not many people complain about Google maps because it is such a good product. But I bet there are some webmasters out there that still need sleeping pills to chase away the bad dreams they have from the day that Google maps was released.