A video posted on Youtube from Transformers: Age of Extinction filming on October 25 at Hong Kong's West Kowloon Cultural District provides a look at what might be the final scene of the movie. It shows Nicola Peltz and Jack Reynor standing behind Mark Wahlberg as he talks up at a pole that represents Optimus Prime while Peter Cullen's voice booms from nearby speakers.
Below is my best guess of Cullen's lines which hint at some movie events so spoiler warning. After that moment other bits from filming at other locations are shown. This is from the same source, LF3258, that show posted video of other TF vehicles earlier in the week. The image on the left of Peltz, Tucci, and Wahlberg's stunt doubles is from a gallery of images you can find here. Great photos of mostly the vehicles on set but no clue what was being filmed.
Update Few more set images, with Walhberg carrying his sword and the cast running with their large bag can be found here.
Prime: There remains a price on my head. I endanger you all if I stay. I shall take it where it will can never be found.
Prime: (?)...can't let them. When look at the stars think one of them as my soul. Defend this family Autobots as they have you. (?)...dear friends how they can be.
Blast of smoke, maybe representing Prime flying off