So having seen a few leaks and other speculation, I wanted to present my theories for the next 2 blocks:
Born of the Gods:
The title suggests this will be about those who are "Born of the Gods," gods given the body of mortals, like Perseus. I'm assuming that the Heroic ability will be expanded more in this. Humans and other "mundane" creatures will appear with impressive abilities, likely many Legendary creatures, and there will be less enchantment creatures.
Journey Into Nyx:
We can guess what the story will be. As for the gameplay mechanics, this would be the opposite of Born of the Gods; taking place in the realm of the Gods themselves, enchantment permanents would be extremely prevalent. Also, some surreal art is likely due. An early leak shows Elspeth and Ajani fighting a huge monster, presumed to be Mogis. We know that Elspeth wrote a letter to Ajani, and Heliod planned to make her his champion, likely sending her to defeat Mogis.
Something else is worth noting: Besides the 5 Gods we got in Theros, several other 2-color Gods were shown:
-Athreos, Ferryman of the Dead (WB)
-Iroas, God of Victory (RW)
-Mogis, God of Destruction (BR)
-Pharika, God of Grief and Old Age (BG)
-Ephara (UW- though the only card to mention Ephara is Ephara's Warden, UW and GW are the only color schemes not to be featured on a Theros card and imply one of the Gods.)
-Keranos, God of Storms (UR)
-Kruphix, God fo Mystery (UG)
-Karametra, God of Agriculture (GW- though there are no GW cards that implicate Karametra, like Ephara, the two that mention her give some pretty clear clues- Setessan Battle Priest is white, and Setessa is mainly a Green city-state, and Bronze Sable mentions Karametra awakening "guardians" in a shrine, a rather GW tactic)
-Phenax, God of Deceit (UB)
Its easily assumable that we'll be seeing them in future blocks. Whether or not they'll all hit in one of the two blocks or if they'll be spread out 5 per block, like Ravnica, is yet to be seen. Also debatable is if they'll function the same as the 5 main Gods, becoming creatures according to your devotion since they're 2 colors.
A notable absence from the God lists is a RG God. However, something I noted (and I'm sure I'm not the only one to see this) is that Xenagos, a RG planeswalker, according to the Theros guide, is attempting to becoem a God. Its entirely possible that he'll be reprinted as a God.
Also, do you think there will be an Artifact God?