Yes, it's true. After many months of debate, Angemon's true mega is revealed. And the winner is:

SERAPHIMON!

This has been confirmed. I don't know what's up with Angedramon, however I do know that Seraphimon happens to be comming up in a certain Digimon movie. ~_^ He along with Gatomon will go mega to fight the enemy...you go, guys!