I've broken down the 134 Trials competitors according to method of qualification. Here are the results:
35 - sub-2:19:00 (the 2012 standard)
63 - 2:19-2:22
28 - downhill courses (not including Boston)
8 - 10k time
134 runners total
Let's say you have a 50% chance of running 2:16-2:19 (if everything goes perfectly-- training, health, weather, etc.) and a 50% chance of running 2:19-2:22. Under the current system, you're virtually assured a place in the Trials. So, it makes sense to devote a good 6 months to marathon preparation.
Now, you're faced with a 2:19 standard. All of a sudden, in a given race, your chances of qualifying are 50%. Does it still make sense to devote 6 months to single-minded marathon preparation? Or does it make more sense now to forget the marathon and pursue the half standard? You can race the half more often, and the performances are generally less volatile from race to race.
Put yourself in the shoes of a 2:19 bubble guy. I'd say these guys are, if anything, LESS likely to devote themselves to marathon training. After all, 20 guys ran sub-1:05 at Houston this year.
You know what they say about the road to hell...
***
I'd be willing wager $100 that more than 50% of the '12 Trials qualifiers do NOT run sub-2:19 during the qualification window.