Other mechanics could be something like a Guardian Angel-type effect:
When ~ enters the battlefield, you may reveal an Angel or Spirit card. If you do, something beneficial happens.
My guess is it will have ways to exile cards from the graveyard then replay them from the exile zone. Sort of a Flashback for exiled cards.
They specifically made the Exile zone to be a place where you couldn't interact with cards. They've stated that the Exile zone is NOT a second graveyard, so anything along those lines is completely out of the question. Exile is either a temporary storage place (Cascade, Oblivion Ring, etc.) or a "your creature's gone and it's never coming back" zone (Path to Exile, Swords to Plowshares.)
I swear I first read it as Wingbonger...something tells me that "As Long as Wingbonger is paired with another creature, both creatures have weed." wouldn't be as good. Seems solid for limited.
I think we will have a returning mechanic that has to do with the graveyard.
My guess is retrace.
When ~ enters the battlefield, you may reveal an Angel or Spirit card. If you do, something beneficial happens.
Lets make dem angels playable!
They specifically made the Exile zone to be a place where you couldn't interact with cards. They've stated that the Exile zone is NOT a second graveyard, so anything along those lines is completely out of the question. Exile is either a temporary storage place (Cascade, Oblivion Ring, etc.) or a "your creature's gone and it's never coming back" zone (Path to Exile, Swords to Plowshares.)
RIP Mike McArtor. The Mothership won't be the same.
Legacy
GG Aggro Elves GG
However, I do think that we will see at least a few cards that exile things in AVR, considering it represents banishment (ie demonslaying)
Another possible candidate for a returning mechanic could be cycling.