Marathon training + intensive swimming - good idea?

Personally I would up it to 4xweek for the running.   Otherwise, I think it's a fine plan.

Marathon training on 3 days/week wouldn't seem like enough to hit your goal.  At least throw in one extra easy recovery run.  Sometimes it's all about the frequency.

And I see no problem with extensive swimming during marathon training.  It's good cross training and it's using mostly upper body.

I like your plan, but a time like that will be a BQ and encourage you to run even more.

Maybe you are the type of runner (athlete) that can use the Runners World "run faster... run less" or something. Its like three quality runs a week. Structured around pacing, tempo, speedwork and of course the weekly long run. Leave you time for a few swim sessions and that stuff about a "Job".

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I'd probably be more help with your thesis than with your run training, but I can tell you that I'll be on a similar path after this weekend (my A race is Sunday), running a marathon in December, but wanting to do some serious swimming as well.  I don't find that swimming affects my run training seriously, as long as I schedule things in a reasonable way.  I'm planning to swim 4 times a week and begin by running 3, but pretty quickly move that to 4, and up to 5 for a while.  I personally find that I make very little progress running 3x/week (though I can maintain running fitness quite easily with that schedule).

I would think the swimming would only help, other than it takes time.  The swims help to loosen your muscles and stretch them out - though I would minimize the kicking on the swim.  In the end, the marathon is about endurance, not so much speed. Tempos and long runs are key to BQ.  Just don't fool yourself by running the long runs slow the whole way.  After the first few, when your body gets used to the distance, begin picking them up for the last 5-6 miles close to or  little under MP.

I think you should be able to do it, if you ran those halfs capping off a HIM.

You can do it, but I don't think you "should".  Run a marathon when you have time to train for it properly. 

Even still, swim 4-5x/wk, run 4-5x/wk and bike 1-3x.  None of the runs or bikes need to be terribly long.  In fact, I wouldn't run much more than 90min or so in any one run.  Do a few miles at tempo pace each week.