Ancient Greenwarden is already labeled as broken by some standard players, alongside Nahiri's Lithoforming spell. But as with many other cards, this doesn't seem to go beyond standard format.
It would be better to play Crucible of Worlds or even Panharmonicon in eternal formats than a 6-mana monster, so financially, this card isn't going to hold its price for too long — unless it breaks commander format as well.
Currently, commander players are pairing it with Lord Windgrace, which benefits well from Ancient Greenwarden's mechanics, so it could be a hit for sure. But that's just speculation at this point.