I see two prospective scenarios that would be different than the current one:
1 - allow all athletes "in" under a certain time standard. If you say that there have been 267 this year, then we can see that there would be somewhere around 300, since "extra" people would go and run sub-2:15 in order to go to the Games.
This presents problems. One, the obvious one that all endurance events would then lobby for increased participation and they would actually deserve it. This would cost a lot. Two, if the race followed form and the winner was the usual 2:09-2:11, there would be a runner through the chute nearly every second for 5 minutes (300 seconds). This would be just meaningless. You would also have guys who deserve to be in the top-10, top-30, or whatever clawing their way through the field instead of racing like normal. Clearly some would have an off-day and finish past 2:15, but not many. I also don't see why the people who have just run 2:14:50 need to be in the race? In this scenario, there would be 200 people in front of them if they ran to form. This wouldn't make it "better" to qualify for the top-50 runners who all entertain hopes of top-10 or 15 but just make it non-exclusive after the guys who have run 2:10 or better.
People will argue that they can fit 255 in the NCAA XC race and that is only 10k. However, there is MUCH more separation in a race like that than there would be in an all-star marathon such as this.
Also, people would trip.
2 - we could do the same as above but lower the cutoff to, say 2:13. Well, that pretty much has all the drawbacks of all the systems ever proposed. The 2:16 marathoner from Ecuador doesn't get to go, people on the bubble work too damn hard and are flat at the Games. I don't see that this one has any merit.
The current system seems to work pretty well. There must be a reason why Abera won so many in a row (in current times) and why there can be so many repeaters over history (Bikila 2X, Shorter 2 medals, Lismont 2 medals, Cierpinski 2X, Wolde 2 medals).
I do strongly support the idea of allowing a team of 6-10 if they are under a certain standard. And dominant runners should be given an automatic entry, perhaps any medallist in the Games or the WC in history should be allowed entry and then your nation could fill out their team of 6-10 on top of that.
I agree that some nations have 15 or so runners capable of going for medals, but allowing everyone under 2:15 in probably would not be the best way to facilitate letting these types in.