There probably won't be white dragons in the game – the fans don't seem to like that idea for the castle, but they might appear as neutral creatures. Griffons are being added as a counter to manticores, creating some symmetry. I'm curious, though: were dragons of light ever mentioned in the lore of Ashan? All the other dragons have their own race and offspring (Silanna has the elves and emerald dragons, Arkath has the dwarves and lava dragons, Malassa has the faceless and black dragons, Elrath has the angels – but where are the dragons of light?

Added 11 minutes later
By the way, it might be better to base the elf dragon summon on the avatar. And the Arantir special ability could be replaced with something else – for example, there's a company where the hero's specialization periodically summons dragons during battle. I think that idea originated from the original Heroes game. Something like that happened during the siege of the city of Biara.