During the charity stream Anet did today one of the devs mentioned there was a, as far as they were aware, undiscovered hint/secret in the End of Dragons trailer.
Some guesses made on reddit include this flag, which is very briefly seen in the trailer
Which appears to be the exact same as the Aetherblade logo
Perhaps they are coming back?
Other possibilities noted are
'MMXXI' written on bell
'Eye' symbol on the top part of first gate at 0:09
The word 'Mercy' on the dragon pipe at 0:21