First off, I have wanted to be involved with this discussion for a while but I had lost my log-in info.

I think a new anime that follows the manga more closely would be fantastic. I am a very big Roy fan and the anime/movie always leave me feeling dissapointed.
A new anime series is always a possibility as some people have previously stated. Some series have had additional series added on over the years to continue what they started and some have had complete remakes. It really is never too late. The Tenchi OVA took 10 years before they finally continued it. And just the past couple of weeks they just started putting out a new Slayers TV series, the last one being years ago (not counting the OVAs). Record of Lodoss War had an OVA and a TV series. The TV took over half way through the OVA and completely re-wrote everything from there.
I could list examples all day but my point is new series and remakes happen all the time. Some completely ignore what has come before them and start over, some just continue where the last left off, and others change and or keep what they want and continue the story.
If FMA were to have a new manga based anime it still doesn't have to follow it exactly frame by frame to still be true to that feeling. There is always room for some changes without going too far off. If the manga is going to end fairly soon it would be quite possible to do it again in two seaons. Or as someone earlier mentioned it is also possible to do a series and a few OVAs or a movie to finish it up. The sky is the limit I am sure you all know. If anyone be it Arakawa or Square Enix or who ever feels there is money to be made I am sure they will do something with it.
For those that commented it would be too much work, I wouldn't consider that to be an issue. It isn't any more or less work to go back and follow the manga than it is for any other series that gets animated. They all get paid either way.
I did enjoy the original anime, it is what got me into FMA. Once I read the manga I was completely drawn in to that version when I saw how much more there was to the story. I really would like to see all that the anime was missing get animated as well as all the characters we didn't get to see.
One more final note on another series they have gone back and redone. Ah My Goddess was originally animated well over 10 years ago. It was too short to be able to faithfully follow the manga. Just a couple of years ago they just went back and made the new TV series to follow the manga more closely. Something like that makes me believe without a doubt that a new FMA anime is even more possible, if not now, some day.