Picking an lord should be like picking a job - you don't ALWAYS rush to where the most money is, but you can.
I'd like to see it stay as it is, but where influential Lords often work for the advancement of their knights. So picking a Lord based on his reputation in the realm can help move you along, giving you a reason to stay with him. And a Lord working on behalf of his knights can build his own power base.
So, instead of this intangible game concept of a "solemn oath", push it more toward players actual making the knight-lord relationship a real one.
I don't know if it will really work out, with the player base issues and things, but that's my argument for leaving as is for now.