Will the new movie use the original theme?

I have no doubt that this movie will have new, original music. Nearly every movie trailer/commercial uses music from another source not actually heard in the movie. Take the example from the many trailers of nearly any movie made in this modern day world.

As for whether or not it will have the classic G theme, if it does I will stand up and clap at the end of the movie!

I'm already too pumped for this movie, I can hardly get anything done! Please don't torture me with this thought! Too late. :(

Its doubtful at best.

BUT, there is always a chance the japanese version will. Japan does have a habbit of occassionally going in with their dubs and changing music scores. They did so a little bit with transformers. 

I think that they may have the original theme or a classic Godzilla theme during the credits. Maybe Godzilla will roar his classic roar we all know and love once in the end before the credits. But probably not.

I highly doubt it. It's a reboot after all.

The Space Oddesy music was only used for the trailers since it captured the right kind of tension and mystery that Legendary was going for.

Alexander Desplat's score is going to be all original as far as we know. It's likely going to be heavily inspired by the original themes, but I doubt they'll use any themes from the Toho series.

If they do borrow any themes, then they'll be sure to remix them to fit in with the music already present in the film. After all, music and score is just as important as the video that it accompanies. The coolest visuals without the right audio is meaningless and has almost no impact to it at all.

To demonstrate, play the extended footage without any audio and see how "cool" it is compared to the video with the audio on.

If the old Godzilla themes don't fit with Desplat's score, then they won't be used.

I can most easily imagine the Godzilla theme being implemented into this soundtrack similarly to how they did the Star Trek theme in the 2009 Star Trek film.  You hear hints of it in certain tracks, with the bits and pieces of the theme becoming more and more obvious as the movie goes on, until the end credits play it full blast in its entirety.  For Star Trek, I know that Michael Giacchino used this approach because he felt the reboot and its new cast had to "earn" the Star Trek theme over the course of the film, which is why I feel that Desplat might do something similar with the Godzilla theme.