I realize that having the knowledge system account wide circumvents some of the ideas that it will be harder when your character is the opposite alignment when traveling opposed lands. With that said SWTOR had a legacy system similar where you obtained achievements that worked account wide. There is really is no advantage to any one character obtaining all the knowledge of every character it just saves time from having to redo the many things you already did on one character to get those knowledge bonuses.
Anyway that's my two cents on this topic
This could actually work in some cases. Meaning eveything should not be account wide, but something really could, just to avoid pure grind.