If you run sub 2:08 on any certified course in the two years before the Games, you are in. 2:22 for women. They could tune these times to get the numbers they want.
My rational:
-The races will obviously not be as good as they could when the current, active, fit, WR holder is not in it.
-Having a trials makes potential runners have two training cycles. The guy who does well at the trials could be ill prepared for the Games or the opposite .
-The field size is essentially unrestricted logistically.
-The justice aspect. Clearly and rightly, there are some heart-broken Kenyans today who could medal, if not win, and should be in London.
If it is a money thing, they could pay the way of the top three from each country or some other plan that does not as cost. The unpaid runners pay their own way.
Finally, how lame is it that a Kenyan might hope to win through the mechanism of a rival not being picked. Really, they gold won't be the gold without Mutai in the race. If he was not there because he failed at a trial or was injured, fine. He is not there because of a political decision.