The problem is not to run 2 marathons in 4 months. The problem is to run one Marathon in Spring (normally London) at 110% of the pressure and as main goal of the season, otherwise a Kenyan can't go in the Team.
This is a situation only Kenyan marathoner have. For example, before London, Tiki Gelana ran very fast in Rotterdam (2:18:58), but without any specific request under the nervous side. Being the criteria adopted by Ethiopians for selecting their team looking at the best times (it was ridiculous to consider, for men, the times of Dubai, leaving Kebede, winner of London, out of the Team...), Tiki knew she could be in the Team running 2:21:30, but didn't have the pressure to beat other Ethiopians having the same goal in the race.
She had pacers, and the only thought was to run fast (the second was the Italian Valeria Straneo, with the National Record of 2:23:44, almost 5 minutes behind).
In the past, for example, Stefano Baldini Always ran London, also when won Olympics, and also the second time he won bronze medal in WCh (2003). But the situation was completely different : he ran at 80% of his shape, using London as "passage" in his plan, with good results (his first 5 personal performances are all in London, and never he was at the top of his personal shape), but without using both during the preparation and the competition too many nervous energies.
If you are a Kenyan, the situation is completely different. You need to be in the best shape of your life for beating the other Kenyans, and the situation of 2012 was very clear.
That year. there is no doubt Wilson Kipsang and Mary Keitany were by far strongest than all the other Marathon runners in the World. However, they were not able to recover the same shape : I remember that, two months after London, in spite of trying their best with full focus on Olympics, they were not able to run in training close the times used before London. This happened not with Wilson and Mary only, but for Edna Kiplagat and Emmanuel Mutai, too. Only Priscah Jeptoo had a good shape, probably because she didn't have too much pressure before London, not having as priority in her mind to compete for being selected, but only for running at her best, and Abel Kirui was at 90% of his shape, after a bad London for typhus problems.
The problem is clear : normally, athletes running at 100% of their shape in London don't have time for recovering the nervous energies they need for preparing Olympics at top level.
On the other side, among these athletes, the best specialists go between 100,000 and 400,000 USD of appearance for starting, their managers sign sontracts already 6-8 months before, and it's difficult to say them "don't run in London".
The situation of Kenyans is that they have so much deep level, that the number 6 or 8, well motivated and properly prepared, can win a medal in Olympics better than the winner of London, if Kenya uses a dry selection at the end of April.
So, I understand the position of AK : they ask to the best runners "Are you interested to run Olympics ? If yes, you can't run any Marathon after the end of February", and the athletes can chose.
But I think one thing can be bettered : the deadline (moving from half of February till the end, for including Tokyo, that is a Major and can be used for winning the jackpot by some athlete),
And, of course, if this rule was released immediately after WCh, at the beginning of September, for athletes and managers the situation could be easier, and also for the organisers of the top Marathons.