For the love of God! Again with the Unicron BS! He is simply too big to be done right. For reference, check out the pic below...
Now, seeing as Prime is 32ft tall in this continuity, that would make that red line 12,800ft tall. That's not even 2.5 miles. For those suggesting that Unicron is the Moon, the moon is about 2160 miles wide or roughly 356,400 time larger than Prime. Anyone wanna try putting those two object on screen effectively? You know, like having a conversation like they did in the cartoon.
If they were to put Unicron on screen, fans are going to want to see him talking to other Transformers. Now assuming that Unicron is the size of the moon, and an average Transformer head measures 3 ft, times 356,000, would make Unicron's head 200 miles high!
Just how would you make that scene work? Prime at 32 ft tall looking at a 200 MILE tall head! Go for it.