I bought general magazine called "Da Vinci" that is member of society-oriented information magazine because there is the feature article of FMA.
Though not all contents, I write the interview of Arakawa-san as follows.

"The ending will become the content that destroys and gets over the principle of the equivalent exchange."

"Mustang battles in Central in the vol. 22 though, the reason that he kills nobody is because 'He looks resolutely forward, so Mustang thinks he had better give the other martialists a clean image to be prepared for becoming a Fuhrer.'"
(Oh, you're useful at detecting those things! )

"Of course, there are some foreshadowing that were originally-conceived, but there are also the another cases".

Those are...

The case that Arakawa-san can't help but make historical ends meet reluctantly as an addition because characters begin to talk a lines automatically.

And the case that Arakawa-san often hunts for the past story and thinks "This is usable for the present story".

For example, the another foreshadowing.
There is the scene that a letter of "HANGAR" is casually written in the background of the Briggs fort.
You know, the airplane doesn't come out to the world of FMA, but when thinking historical backdrop, the Wright brothers already succeeded in a power flight before starting the story of FMA.
Therefore there is the possibility the airplane is also developed in the world of FMA, and an airplane may fly in a story aftertime.
The reporter says like this foreshadowing that readers accidentally can't help but guess or imagine is very interesting.  

"I wanted to show the thing the minor figure also does one's best, and I'm surprised myself that Darius and Heinkel take charge of very active part more than I imagined."
"Because I was brought up in the society which both an adult and a child work, I can't imagine the person who doesn't work ( NEET or stay-at-home). It's so hard for the farmers to be able to readily progress the work if there is not a family in a body."
(I think therefore it's felt that many female characters of FMA independently have a job. )

"I scanned through Gangan before my serialization lightly and thought about how I could make my work stand out in Gangan thoroughly. There were many works which used many screen tones, so I consciously increased the scenes that used all one color, and when color painting, I did it with not CG but thickly-painted paints, too. I struggle to survive!"
(Um, Arakawa-san is originally weak in CG though? )  

"Because there will be the people who read Gangan, plus buy my comics, I think an omake is very important, and I was so once. I still can't shed the feeling of a reader."
(Excellent! )

"I don't understand clearly why FMA had a success. Because a leading character already has a excellent ability, only adults are around him and a subject is fanatic-oriented, I thought it was enough if appealing a little to some people. But I felt pressed to have to draw the manga soon because alchemy is an interesting subject! Basically the alchemy will be indoor though, I like outdoor activity and wanted to draw the manga that everything comes out from a wall or a floor, so I tried to mix those."

"I make a point of inserting my both good and bad sense of value in all characters. 'Becoming a martialist who legally can carry it out so that it isn't accused of a crime even if he tries his deadly ability to  people' of Kimblee is my unpleasant sense of value. Kimblee also chose the method after all to satisfy his desire in a rule of the society because nobody can live if not getting the viewpoint that conformed to some sort of social rules."

"The ending will become a little long way off than I thought because the stories that I want to draw have increased."

Almost it's like this.

I'm in it.